Answer:
1. Non equivalent, use the distributive property. 5*3=18, 5*4=20, so the equation is now 18y - 20, which is not equal to 15y - 20
2. Same with this one, -4 * -2p = 8p, and -4 * 4 = -16. Now the equation is 8p - (-16), or 8p + 16. Not equivalent.
3. 3*-7x = -21x, and 3*13 = 39. Now the equation is -21x - 39, not equivalent.
4. -6*-4a = 24a, and -6*8 = -48, the equation is now 24a+ (-48), or 24a - 48
I did my best, and I am confident in the answers, but I apologize if I am wrong.