Solve the equation -15=a/5 a=-3 a=-20 a=-10 a=-75

To solve any equation, you do whatever you need to do 
to wind up with the unknown quantity all alone on one side.
BUT ... whatever you do to one side of the equation, you must
also do to the other side.

Here, we have the
he original equation:           -15  =  a/5

Multiply each side by 5 :     -75  =  a

and bada-bing, THERE's the solution !

The answer is why would a teacher ask that