75 students decreased by 80%

I'm confused on this could anyone me and show me what i need to do to solve it.

Worth 15 points handsome jack is buying a pony made of diamonds. the price of the pony is p dollars, and jack also has to pay a 25% diamond pony tax. which of the following expressions could represent how much jack pays in total for the pony? a= p = 1/4 b= p+0.25p c=(p + 1/4)p d=5/4p 0.25p choose 2 answers

Using elimination, what is -4x+2y=-12 4x+8y=-24