What is the first step in solving the problem 3/4 + 1/8?

The first thing you should know is that there are many ways to solve this problem.
 One of the ways, for example, is a simple addition of fractions.
 We have then:
 Step 1:
 Cross product
 3/4 + 1/8 = ((3 * 8) + (1 * 4)) / (4 * 8)
 Step 2:
 Rewrite
 ((3 * 8) + (1 * 4)) / (4 * 8) = (24 + 4) / (32) = 28/32
 Step 3:
 simplify
 28/32 = 14/16 = 7/8
  
 Step 1: 
 Cross product
 3/4 + 1/8 = ((3 * 8) + (1 * 4)) / (4 * 8)