Question 2483
for y: just put everything that is not y to the other side.

1)y - 3x = 7
or y = 3x + 7

2) 2x + y = 5
or y = 5 - 2x

for a: just put everything that is not a to the other side

a + 3b = -2 
or a = -2 - 3b

Greets
Pieter Gurdebeke