Final answer:
The cost of the fort should be no more than $720 in order to allocate enough budget for the swing set.
Step-by-step explanation:
Let's represent the cost of the fort as x.
According to the given information, the cost of the swing set should be at least one-fourth as much as the fort.
So, the cost of the swing set would be 1/4x.
Since the budget for both the swing set and fort is $900, we can set up the equation:
x + 1/4x = 900
Combining like terms, we get 5/4x = 900.
To solve for x, we can multiply both sides of the equation by 4/5.
x = (900)(4/5) = 720
Therefore, the cost of the fort should be no more than $720 and the remaining budget for the swing set would be $900 - $720 = $180.