Set up an equation and solve, or find a common sequence.
We can set up an equation like so, using x = 1 as a base:
x(number) + (another number) = y
translate to:
1(x) + (number) = 5
The common difference is 2 for each y value, so let's use that as a multiplier:
1(2) + number = y
2 + x = 5
x = 3
So lets move up a step:
x = 2 and y = 7
We use 2 as our multiplier and 3 as our adder:
2(x) + 3 = y
2(2) + 3 = 7
4 + 3 = 7
Lets try one more case :
x = 4 and y = 11
2(4) + 3 = 11
8 + 3 = 11
11 = 11
