Answer:
x = 16
Explanations:
The given rquation is:

Step 1: Cross multiply the equations. That is 28 multiplies 4 and 7 multiplies x:

112 = 7x
Step 2: Divide both sides by 7

16 = x x = 16
2,6,15,31,......
6-2=4=2X2
15-6=9=3X3
31-15=16=4X4
So the next number should be 31+5X5=56
hope this helps :)