Whats the area of a square computer screen euth 21 inch sides

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

The cost for an uberi is $2.50 plus $2.00 mile. if the total for the uber ride was $32.50, how many miles did the customer travel?

The sum of the first eight terms of an arithmetic progression is 9m + 14. the fifth term of the06 progression is 2m - 6, where m is a constant.given that the first term of the progression is 26,find the value of the common difference, d and thevalue of m.