This is how you can solve it;
5 = 15y
5 ÷ 15 = y (did the inverse operation of the variable)
0.33 = y or y = 0.33 (rounded to the nearest hundredth)
To check your answer just substitute the value of y in the equation;
5 = 15y
5 = 15(0.33)
5 = 5
so your answer is correct! :D Hope that helps!