" 100% " means "the whole thing",
and "is" can be replaced by "is equal to".
You have said "The whole thing of a number is equal to 61."
or
"61 is equal to the whole thing of a number."
The only number that 61 can be equal to is 61.
H = V/B

The base of the prism is given by the expression 2X^2+8x-9
then c)5x+3
False because it would be 4(2)=4 which is not correct