7=12
-10,6 : 8
(2x/3)^-2
solve (248+x/5)=51
1/2x+1/3 y=5
1/4 x+y=10
solve by substitution
1/4x+y=10
solve (248+x/15)=51
2x/3^-2
1/2x+1/3 y =5
2^-2n(2n +1) =2^-2n
