PLZ HELP, the question is in the picture

Dakota earned $7.50 in interest in account a and $18.75 in interest in account b after 15 months. if the simple interest rate is 4% for account a and 5% for account b, which account has the greater principal? explain. to make it a little easier, there is an image. good luck!

Last one and the bottom answer choice is y=(x-4)^2+1 you guys!

Can someone me with #s 8, 9, and 11. with just one of the three also works. prove using only trig identities.