I've been stuck for 30mins

if f(x) = 3x + 10x and g(x) = 2x – 4, find (f + g)(x)

Nick and nora are married and have three children in college. they have an adjusted gross income of 47,400. if their standard deduction is 12,600 itemized deductions are 14,200 and they get an exemption of 4000 for each adult and each dependent what is their taxable income

Ineed i been stuck on this question since yesterday

If the sales price of a dvd is $20 and the markup is 34%, what is the cost of the dvd?