What is the cost c (in dollars) for the care and maintenance of a horse and carriage is c+15x+200 where x is the number of rides.
write an equation for the revenue r in terms of the number of rides.
r=
how many rides are needed to break even?

You didn't specify how much is charged per ride to determine revenue...but we can just use a variable p for the price charged per ride...

r(x)=px, c(x)=15x+200

To break even, P, profit must equal zero and P(x)=r(x)-c(x)

P(x)=px-15x-200

P(x)=0 when x(p-15)-200=0

x=200/(p-15)

So the number of rides needed, x, can be found once you determine what is charged per ride. :D  *note from even this partial answer that p must be greater than 15 or you will never break even.