you are trying to solve for Z
so now you will do is add like terms
2.4z+1.2z=3.6
now you have
3.6z-6.5=0.7
now you will add
6.5+0.7=7.2
now you will have
3.6z=7.2
now you will divide
7.2/3.6=2
so now you have
z=2
that is all you have to do for salving for z
hope that this helps you