I would divide the number by 4, and then subtract 1.5 and.5 for the first two numbers, then adding .5 and 1.5 for the third and fourth numbers.
Let n be the first number. Then the next number is n+1. Then n+2 and n+3. So:
So, if x is 10, then n is 1. If you're using x,y then y=4x+6. So, 50=4x+6; 44=4x, x=11, and the four numbers are 11,12,13,14. Etc......
Given below is a figure. You have to fill in the numbers from 1 up to 16 in such a way that you get 29 when you add the numbers in each row.