Question 64984
For a slope of 3/4 the stair can rise 3 units for every 4 units of width.
In the case of a 10 inch wide stair then it can only rise a maximum of 7.5 inches to the next step.

If you have 9 feet to go up then that is 9 x 12 = 108 inches.
Dividing 108 by 7.5 gives 14.4.
A greater number of steps will reduce the rise so use 15 steps.
108/15 = 7.2 so use a rise of 7.2 inches.

Note that 7.5 is the maximum rise so any whole number of steps greater than 14.4 could be used and still meet the conditions.