There are two methods to do this;
1.) For this equation, it is easier to cross multiply, which means (32 times z)=(25 times 24)
25 times 24=600
600/32=18.75
2.) You could try and find a common denominator by dividing the left side by 3 and the right side by 4 to have a common denominator of 8.
(z/3)/8=(25/4)=8
Because the denominators are the same, this means the numerators must be the same for the equations to be equal to each other.
So, z/3=25/4
Cross multiply, and you get 4z=75, z=18.75
I recommend the first way how to do it, but it is all up to you. Hope this helps.