Can someone me solve and explain?

question:

suppose a different tournament that eddie organizes has 120 players and the entry fee is $40. each time he increases the fee by $5, he loses10 players. determine what the entry fee should be to maximize the value of the pool.

distance covered by pamela in 9 l of fuel = 99km

let us apply unitary method here.

distance covered by pamela in 1 l of fuel =99/9 =11 km

now let us find distance covered by pamela if she has 12 l of fuel.

distance covered in 12 l = distance covered in 1 l of fuel * 12

we know that distance covered by here in 1 l is 11 km.

so distance covered in 12 l of fuel = 11*12 = 132 km.