Instructions: This task involves creating questions from a given passage that involve some kind of complex reasoning (including numerical reasoning).
The generated questions must require looking at more than one part of the passage to answer. Try to use a variety of reasoning types in your questions (some of the sample reasoning types are illustrated in the 'positive examples' field) and also have a variety of answer types (spans, numbers, dates). A span is a continuous phrase taken directly from the passage or question. In such questions, the answer spans are recommended to be five words. Questions with answer type "number", are expected to start with "How many". For instance, "How long did an event last?" can be phrased as "How many years did an event last?". To increase diversity, try to create more questions for which the answer will be multiple spans. Please create questions that require AT LEAST 2 arithmetic operations as illustrated in the 'positive examples' field. You are encouraged to try DIFFERENT COMBINATIONS of operations and not just limit to the combinations shown in those examples. The more challenging questions you create, the better it is.
Input: Passage: By 1474, cannons had been introduced in Mdina. Other extensive preparations for an attack were made in the 1480s, when the fortifications were once again improved under the direction of Sicilian military engineers. At this point, some buildings in Rabat were demolished to clear the fortifications' line of fire. By 1522, the fortifications were being modernized with the construction of embrasures. However, the walls were still regarded as obsolete, since they lacked bastions and could not resist bombardment from modern artillery. Most of the medieval walls of Mdina were gradually dismantled between the 1530s and 1720s, when the city's fortifications were being upgraded by the Hospitallers. One of the most significant visible remnants of the medieval fortifications is the Greeks Gate and the surrounding curtain walls, which still retains its medieval form apart from the outer portal which was built in the 18th century. Parts of the double walls, including the remains of two gun loops, still stand between the gate and the Torre dello Standardo. Most of the northern and eastern walls date back to the medieval period, although some sections were rebuilt by the Hospitallers. The northern ramparts contain a medieval wall tower, while the remains of Byzantine antemurals and the foundations of a late 15th-century artillery platform have been found in the eastern walls.
Output:
How many decades did it take to gradually dismantle the medieval walls of Mdina?