Which pair of
expressions are
equivalent?
A. 8(2r) and 10r B. 6r + 3 and 9r
C. 9(3r-4) and 27r - 36
D. r+r+r+r+r and r^5

Well...

A.

8(2r)       &     10r

This is incorrect because the second option would be if you added 8r to 2r, not multiplied 8 to 2r.

B.

6r + 3     &     9r

This is incorrect because you cannot add the 3 to 6r, because they are different.

C.

9(3r-4)    &     27r - 36

This is correct because the two options are equivalent.

D.

r+r+r+r+r &     r^5

This is incorrect because the first part would need to be r x r x r x r x r for it to be true.

yw.

Here's x and y for each equation:

x + 7y = 8

x = -7y + 8
y = -x/7 + 8/7

3/8x + 1/3y = 17/24

x = -8y/9 + 17/9
y = -9x/8 + 17/8

Now to plug in!

x + 7y = 8
-8y/9 + 17/9 + 7y = 8
y = 1

x + 7y = 8
x + 7(-9x/8 + 17/8) = 8
x = 1