Simply the following expression: 12x + 5x - 8x

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

Ariel is working at a meat packing plant for 5 nights a week. her regular wage is $11 an hour. she earns tine and a half for any overtime hours. this week she worked 9 hours of over time .how much will ariel earn for overtime this week ?

If cos(2x) = tan^2(y), show that cos(2y) = tan^2(x).