5 x + 18 + 20 y = 43
5 ( x + 4 y ) = 43 - 18
x + 4 y = 25 : 5
x + 4 y = 5
_____________
15 x + 38 + 60 y = 113
= 15 ( x + 4 y ) + 38 =
= 15 × 5 + 38 =
= 75 + 38 =
= 113
