How do i solve this pls help me i got 30 mins left :(

Acircle has a circumference of 28.36 units what is the diameter of the circle

Asmall business produces and sells balls. the fixed costs are $20 and each ball costs $4.32 to produce. each ball sells for $8.32. write the equations for the total cost, c, and the revenue, r, then use the graphing method to determine how many balls must be sold to break even.

How long must $542 be invested at a rate of 7% to earn $303.52 in interest? in a easier way