Can someone PLEASE help me And I will give! I don’t know if it’s the 2nd or 3rd one

Find the solution of this system of equation -7x+y=-20 9x-3y=36

In which form is the following function written? y = - 2(x – 3)(x + 5)

1- what do you think the product of a nonzero rational number and an irrational number is? is it rational or irrational? make use of variables, the closure property of integers, and possibly a proof by contradiction to prove your hypothesis.2- why do we have to specify that the rational number must be nonzero when we determine what the product of a nonzero rational number and an irrational number is? if the rational number were 0, would it give us the same result we found in the first question?