Question 64985
Let's choose the working unit to be inches; therefore, height = 9 feet = 108 inches
Let x be the number of stairs. Each stair has a depth = 10 inches. We can therefore say that the horizontal length = 10*x 

Slope = 3/4 = (y2-y1)/(x2-x1) = 108/10x. 
If we solve for x: x=14.45
In order to see whether we need 14 or 15 stairs we need to try calculate the slope for both cases. 
x = 14 implies slope=108/10*14=0.77
x = 15 implies slope=108/10*15=0.72
We know that the slope should not exceed 3/4=0.75 and therefore we choose x=15 no of steps. 


Cristiana