Is it supposed to be 15 = -4(a-5)? There has to be an equals sign to solve an equation.
If so then you have to isolate the variable (a).
You would multiply -4 by (a-5) separately becoming... 15 = -4a +20
Then subtract 20 from both sides of the equation(equals sign) then it becomes...
-5 = -4a
Now finally we want to separate the -4 from the (a) to figure out what it is. To do that, divide both sides of the equation by -4. -4 over -4 cancels each other out leaving you with only (a) on the right side.
The final answer being... a = 5/4(the two negatives cancel each other) or 1 1/4
Hope that gives you a better understanding even if I didn't answer your exact question.
