Your school is getting a 10,000 seat stadium to hold spectators for your home football and baseball games. For each row of seats, which rise like stairs, the dimensions are 30 inches wide and 12 inches deep. What is the pitch(angle) by which the rows of seats rise from the bottom toward the top?

Isn't slope = rise/run ?

And we do know the rise and the run.
So slope = 12/30 = .4
Since tan (angle) = slope
tan(angle) = .4
angle = 21.8ยบ