To answer this question, you will represent the amount of yards rushed by each running back.
x - Running back #1
9x - Running back #2
The combined yards was 1550, so put these together in an addition equation with a total of 1550. Solve for x.
x + 9x = 1550
10x = 1550
x = 155
Running back #1 rushed 155 yards, and running back #2 rushed for 1395 yards.