Answer: 11 boxes of cards for $72
Step-by-step explanation:
Brennan's equation would be
y=6x+6
Gabriel's Equation would be
y=5x+17
when they spend the same amount the equations will be equal
6x+6=5x+17
x+6= 11
x=11
so 11 boxes they would spend the same
To figure out cost, put 11 into the first equations
y=6(11)+6= 66+6= 72
y=5(11)+17= 55+17 = 72
so they each spent $72
so our slope is undefined, that means a vertical line, check the picture below
