a stone mason builds 7 houses in 3 days. How many days does it take to build 11 houses?

a stone mason builds 7 houses in 3 days. How many days does it take to build 11 houses?

The build rate of houses per days is proportional. Set up a proportion of houses to days where d is the number of days it takes to build 11 houses:
7/3 = 11/d

Cross multiply:
Numerator 1 * Denominator 2 = Denominator 1 * Numerator 2
7d = 11 * 3
7d = 33

Divide each side of the equation by 7:
7d/7 = 33/7
d = 4.7142857142857