Solve the system by substitution.
3x + y = 20
-7y=x

Please help

9514 1404 393

  (x, y) = (7, -1)

Step-by-step explanation:

The expression for x makes it easy to use that for substitution.

  3(-7y) +y = 20

  -20y = 20 . . . . . collect terms

  y = -1 . . . . . . . . . divide by -20

  -7(-1) = x = 7 . . . use y in the second equation to find x

The solution is (x, y) = (7, -1).

  or  

step-by-step explanation:

if the four friends split the cost, p, of the pizza evenly, then each friend pays one-fourth of the cost of the pizza.

the expression is   or  

3/20

step-by-step explanation:

well, there are 20 outcomes, and 3 of them you want. so, 3/20