Your question says
6x + 8y = 12........... Equation 1
y = 2x + 18............. Equation 2
Now substitute y in place of 2x + 18 in equation 1
So we have;
6x + 8 ( 2x + 18 ) = 12
Using BODMAS, solve for bracket.
6x + 16x + 144 = 12
22x + 144 = 12
Carry 144 to the LHS then the sign will change from + to – that will be,
22x = 12 – 144
22x = –132
Divide both side by 22
x = – 6
Now substitute – 6 for x in equation 2
y = 2 ( – 6 ) + 18
y = – 12 + 18
y = 6
So therefore
x = – 6 and y = 6.
