How exactly do you work this out?

7(h + 3) = 6(h - 3)

Starting on the left hand side of the equation, distribute the 7 by multiplying it by each term inside the parenthesis (h + 3):

**7(h + 3)** = 7·h + 7·3 = **7h + 21**

Looking at the right hand side of the equation, distribute the 6 by multiplying it by each term inside the parenthesis (h - 3):

**6(h - 3)** = 6·h - 6·3 = **6h - 18**

Now we arrive at the following:

7(h + 3) = 6(h - 3)

7·h + 7·3 = 6·h - 6·3

**7h + 21 = 6h - 18**

The goal is to solve for the unknown variable, h. To do so, we want to isolate it to one side of the equation by moving all term that contain this variable to one side of the equation and moving all other terms to the other side of the equation, combining like terms as we go.

With this, we first subtract 6h from both sides of the equation and then subtract 21 from both sides of the equation:

7h + 21 **- 6h** = 6h - 18 **- 6h**

**7h - 6h** + 21 = **6h - 6h** - 18

**1h** + 21 =** 0** - 18

**h + 21 = - 18**

h + 21 **- 21** = -18 **- 21**

h + **0** = **-39**

**h = -39**