What is the most logical next event?

How to improve mental math skills
Visualize the equation in your head.
The first step in solving a math problem in your head is to visualize the problem mentally. Imagine the numbers and the equation in your head.
As you solve portions of the problem, visualize the new numbers that you're working with. Repeating numbers mentally or verbally, in a whisper, will also help you to remember more significant numbers in the equation.