1/4c+ 3d when c=6 and d=7

What is the best way to answer questions with a x expression in the question. for example 3x + 10x=?

The difference of three and the reciprocal of a number is equal to the quotient of 20 and the number. find the number.

Currently, the largest cruise ship has a tonnage of 225,282 gross tons (gt). which of the following is a reasonable estimate for the tonnage of this cruise ship? a. 2 × 10^5 gt b. 2 × 10^6 gt c. 2 × 10^-5 gt d. 2 × 10^-6 gt