For 1 step we have to go the 10 feet, then up one foot, and two more feet to cover the step.
f(1) = 10 + 1 + 2 = 13
Write 13 in the first box under 1.
Each additional step requires going up 1 and across 2, 3 more feet total. So under 2 write 16, then 19, 22, 25, 28, 31, 34 for the rest.
In general
f(n) = 3n + 10