What is 5(12-3p)=15p+60 what is 3(y-2)=6(y-1)-3y what is 3a+21=7-4a and explain

#1: p=0
#2:all real numbers
#3: a= -2

First one is -30p = 0 because distribute 5 to get 60 - 15p and its the same on both sides except for one sign. 
second has infinite solutions because distributing gives 3y - 6 = 6y - 6 - 3y. Combine like terms to get 3y - 6 = 3y - 6. When the equation has a number equaling another number there are infinite solutions. 
Third one is a = -2 because if you add 4a to both sides you get 7a + 21 = 7. Then subtract 21 from both sides to get 7a = -14. then divide by 2 to get the answer.