Please help! gkdfjvndfjb gf i hate math with my entire being

Translate the word phrase into a math expression. 15 fewer than the product of 4 and a number. (pls immediately)

Tim's phone service charges $26.39 plus an additional $0.21 for each text message sent per month. if tim's phone bill was $31.64, which equation could be used to find how many text messages, x, tim sent last month?

Which expression is the factorization of x^2+10+21