When rearranging or transposing an equation, you always have to try and get the letter you want on its own by doing the opposite of each step on both sides. In this case it is g:
p= 5gh
Because g is being multiplied by 5 and h, you'd want to divide by 5 and h to get g on its own: (division is represented by the slashes / ).
p= 5gh/5h
Now you can cross off 5h completely from the right side of the equation because they cancel out.
p/5h = g
Because you did that, you have to do it on the other side too so that is why it is P/5h on the left.
