Help fast worth 6 points

Can someone pls ! pls answer all. no explanation needed..

Marco has $38.43 dollars in his checking account. his checking account is linked to his amazon music account so he can buy music. the songs he purchases cost $1.29. part 1: write an expression to describe the amount of money in his checking account in relationship to the number of songs he purchases. part 2: describe what the variable represents in this situation.

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