Well, let’s start with simplifying both of them. 3(5x) simplifies down to 15x. For (3*5)(3*x), you have to use FOIL. Using FOIL you get 9+3x+15+5x, which by combining like terms you get 8x+24. These are clearly not equal (equivalent). You can explain that solving them produces different results and give the process I used to solve both of them.