The essence of air defence is to detect hostile aircraft and destroy them. The critical issue is to hit a target moving in three-dimensional space; an attack must not only match these three coordinates, but must do so at the time the target is at that position. This means that projectiles either have to be guided to hit the target, or aimed at the predicted position of the target at the time the projectile reaches it, taking into account speed and direction of both the target and the projectile.
Projectiles must either be guided to the target or aimed where?
at the predicted position of the target at the time the projectile reaches it

Windows 8 was distributed as a retail box product on DVD, and through a digital download that could be converted into DVD or USB install media. As part of a launch promotion, Microsoft offered Windows 8 Pro upgrades at a discounted price of US$39.99 online, or $69.99 for retail box from its launch until January 31, 2013; afterward the Windows 8 price has been $119.99 and the Pro price $199.99. Those who purchased new PCs pre-loaded with Windows 7 Home Basic, Home Premium, Professional, or Ultimate between June 2, 2012 and January 31, 2013 could digitally purchase a Windows 8 Pro upgrade for US$14.99. Several PC manufacturers offered rebates and refunds on Windows 8 upgrades obtained through the promotion on select models, such as Hewlett-Packard (in the U.S. and Canada on select models), and Acer (in Europe on selected Ultrabook models). During these promotions, the Windows Media Center add-on for Windows 8 Pro was also offered for free.
During it's launch how much was a Windows 8 upgrade?
$39.99 online, or $69.99 for retail box

By April and May 1941, the Luftwaffe was still getting through to their targets, taking no more than one- to two-percent losses on any given mission. On 19/20 April 1941, in honour of Hitler's 52nd birthday, 712 bombers hit Plymouth with a record 1,000 tons of bombs. Losses were minimal. In the following month, 22 German bombers were lost with 13 confirmed to have been shot down by night fighters. On 3/4 May, nine were shot down in one night. On 10/11 May, London suffered severe damage, but 10 German bombers were downed. In May 1941, RAF night fighters shot down 38 German bombers.
How many German bombers were shot down by the RAF in May?
38 German bombers