If i can see it right, it would be A because it starts at 30, then rises as the number of rooms increases.
3x + 9 = 10 + x
2x +9 = 10
2x = 1
x = 1/2
<span> (3x</span>² <span>+ 8) - (2x</span>² <span>+ 1)
= </span>3x² + 8 - 2x² - 1
= 3x² - 2x² + 8 - 1
= x² + 7
