Help me pleas and explain how it is that answer thanks

What value of x is in the solution set of –5x – 15 > 10 + 20x?

Ricky takes out a $31,800 student loan to pay his expenses while he is in college. after graduation, he will begin making payments of $190.66 per month for the next 30 years to pay off the loan. how much more will ricky end up paying for the loan than the original value of $31,800? ricky will end up paying $ more than he borrowed to pay off the loan.

Cos^2x+cos^2(120°+x)+cos^2(120°-x)i need this asap. pls me