Answer: This is a system of equations, let's set it up. I set the variable for 1 story houses to x and 2 story houses to y. Here are the two equations:
6x + 2y = 72
5x + 7y = 124.
Now we multiply the equations so that when we add them together one of the variables will be cancelled out. I am going to multiply the top equation by 7 and the bottom equation by -2. This gives us
42x + 14y = 504
-10x -14y = -248
Add the two equations together:
32x = 256
Divide by 32 to get x = 8. The one story houses have 8 doors. We can plug this number into one of the original equations and solve for y now. I'm going to use the first equation.
(6*8) + 2y = 72
Now we solve for y
y = 12 So, the 1 story houses have 8 doors and the 2 story houses have 12 doors.