You can find the unknown side length by using pythagorean theorem. a²+b²=c²
Simply plug-in numbers into the formula. Your answer is 80.
2p+6a=$14
3p+9a=$21
3p+9a=21
Subtract 9a
3p=21-9a
divide all by 3
p=7-3a
plug it into start equations
2p+6a=14
2(7-3a)+6a=14
14-6a....+6a=14
this zeroes out...
The answer is a because it has a negative slope and to find it i did rise over run it rises one block for every four it goes over