How would I convert this equation from polar form to Cartesian/rectangular form? My book gives the answer in the index, but doesn't explain how to get it, and I've been trying multiple ways of solving it.

If 10 men take 18 days to mow 60 acres of grass, how long will 15 men take to mow 80 acres?

Galen sold tickets of his church’s carnival for a total of $2,820. children’s tickets cost $3 each and adult tickets cost $5 each. the number of children’s tickets sold was 30 more than 3 times the number of adult tickets slod. how many children’s ticket and how many adult tickets did he sell?

You got a job selling magazines door-to-door. you are paid $100 per day plus $1.50 for each magazine you sell. which recursive formula models this situation?