How many ways can a librarian arrange 15 books on a top shelf if she has 20 books from which to pick?
20! /5!
20! /15!
15! /5!

x = -3

y = -18

step-by-step explanation:

to solve by substitution, substitute one variable and solve for the other. then substitute again to find the remaining variable.

x-1/3(3x-9) = -3 since y=3x-9 substittute y.

x-1/3(3x-9)=-3

x + x +3 = -3

2x+3=-3

2x+3-3= -3-3

2x=-6

x=-3

substitute again into y=3x-9

y=3(-3)-9

y=-9-9

y=-18

1

x = 1

step-by-step explanation:

0 ÷ x = 0

0 ÷ 1 = 0