A plumber charges a service charge of $20 plus $15 per one-half hour of work. the cost to hire the plumber is given by the function f(x) = 15x + 20, in which f(x) represents the cost and x represents the number of one-half hours the plumber works. If the Jackson family has $200 to spend on the water leak repair, what is the maximum number of hours the plumber can work to repair the leak?