How do i solve 5y - 10 = -25?

So to find the answer you want to isolate the y. So the first thing you want to do is to move everything to the opposite side of the = sign. You start by adding 10 to both sides.
10+ 5y -10 = -25 +10  
 5y = -15.
the tens cancel out on the left side and on the right you get left with -15/
Since y is being multiplied by 5 you always want to do the opposite so you divide by 5.
5y/5 = -15/5
y = -3
It's hard to explain but you just have to remember that what you do to one side you must do to the other to keep the equation balanced.

5y - 10 = -25

First, add 10 to both sides. / Your problem should look like: 5y = -25 + 10
Second, simplify -25 + 10 to get -15. / Your problem should look like: 5y = -15
Third, divide both sides by 5. / Your problem should look like: y = 
Fourth, simplify  to 3. / Your problem should look like: y = -3

 y = -3

3were boys and 5 were girls