When is the value of 6(x +15)-12 When x=12
6 x +90-12
6x=78
x=13
is this right
No. They're not asking what x is . They told you it is 12!
6x+90-12
6*12+90-12
72+90-12
150
Or,
6(x+15)-12
6(12+15)-12
6*27-12
162-12
150
6 x +90-12
6x=78
x=13
is this right
6x+90-12
6*12+90-12
72+90-12
150
Or,
6(x+15)-12
6(12+15)-12
6*27-12
162-12
150