Solving
the equation -3(y - 5) = 24

Distribute
-3y+15=24
      -15=-15
-3y=      9
-3      =    -3
y=-3

-3(y-5)=24
First follow the distributive property and do the parentheses. 
-3 times y gives you:-3y 
-3 times -5 gives you 15 since a negative times a negative is a positve. 
So now you have -3y +15 = 24
subtract 15 from both sides and you will get: -3y+15-15=24-15
which then gives you: -3y= 9
to get y by itself divide both sides by -3. 
this gives you: y= -3