Solve it simultaneous, 4a+6a=21and7a-3y=3

Answer 1

Looks like a typo to me, is the first equation 4a + 6y = 21 ?
if so, ....
multiply the second by 2 -----> 14a - 6y = 6
add this to the first
18a = 27
a = 27/18 = 3/2

sub this into 4a + 6y = 21
4(3/2) + 6y = 21
6y = 21 - 6 = 15
y = 15/6 = 5/2