Pi(r^2)(12)=324 , how do you find the radius of this equation?

If f(x)=2x-6 and g(x)=3x+9, find (f-g)(x)

Need solving this second acceleration problem.

Josh has a rewards card for a movie theater he receives 15 points for becoming a rewards card holder he earns 3.5 points for each visit to the movie theater he needs at least 55 points to earn a free movie ticket which inequality can josh use to determine x, the minimum number of visits he needs to earn his first free movie ticket.