Answer:
B
Step-by-step explanation:
In order to combine like terms, they must share the same variable. We can't combine things 9y and 3p because they contain two different variables. On the other hand, 7r and r work because there is only one. 7r and r combine to 8r+2
multiply the height x the length x the width to find the volume of a room (or another 3d object)