Algebra Simplify and Substitution

If a=12, work out the value of:

3a - 15 =

If a=12, work out the value of:

4(a - 15) =

If g=3 and h=6, work out the value of:

2g - 3h =

If g=3 and h=6, work out the value of:

3g + 2h =

If g=4 and h=7, work out the value of:

gh - h =

If g=3 and h=6, work out the value of:

2gh + 3g =

If g=3 and h=5, work out the value of:

4h - 2gh =

4a-b=?

when a=3 and b=5