Solve.

4x + 4y = 20
4x + y = -10

The way I'd do this is by elimination.  Multiply 4x+y=-10 by -14x+4y=20-4x-y=105y=30y=6
As for x multiply 4x+y=-10 by -4
4x+4y=20-16x-4y=4012x=60
x=5

The answer is ( first we looking for what is the "x" and what is the "y" )we have same number for x. but both of them is positive so we have to make different sings let's do { 4x+4y=20 ) the next side we multiply by negative sing ( -4x-y=10 ) now subtract ( 4x-4x ) is gone  ( 4y-y ) is 3y ( 20+10 ) is 30. what we have finely ( 3y=30 ) now solve "y" divide each side by 3 ( y=10 ) we get "y" so now we look for "x". we take the orginal question ( 4x+(10)=-10 ). "y" we plugging 10 ( 4x+10=-10 ) now solve "x" ( 4x=-20 )  then divide each side by 4 ( x=-5 ) now we get "x" right so the answer is ( x=-5 , y=10 ) that sad. i hope you understand what i did   

Ac equals 35 cm long