Let, x be the maximum hours he can rent skate board and helmet.
So, total price :
T = 4x + 6x
Now, it is given that he has only $30.
Therefore,
Total price should be less than or equal to $30.
4x + 6x ≤ 30
10x ≤ 30
x ≤ 3
Therefore, the maximum number of hours he can rent the skateboard is 3 hours.
Hence, this is the required solution.