f(5) means to replace the x in the equation with 5.
f(5) = 8(5) - 3
f(5) = 40 - 3
f(5) = 37
N is 7.5 because prq is 3x the size of abc
Estimation can be very useful because when we do not know the actual correct answer we can just estimate. Estimation helps you check your answer by seeing if the estimate is close to the result you got. You can also estimate first to know approximately what result you should expect to get.
