Question 200430
(1)  a+b = 2a -15,,,,,,-a+b =-15
.
(2) a-b =2b-5,,,,,,,,,,,,,a-3b = -5
.
add(1) + (2),,,,,,,,,,,,,,,,,,-2b = -20
.
b= 10
.
substitute  in (1)  -a +(10) = -15
.
-a = -25
.
a =25
.
check (1)  25 +10 =2*25 -15 =35 ,,,ok
.
(2) 25 -10 = 2*10 -5 = 15,,,,,ok