To determine the maximum number of boxes the truck can carry while still being able to cross the bridge, we can set up an inequality based on the combined weight of the truck and the boxes.
Let \( b \) be the number of boxes the truck is carrying.
- The weight of the truck is 40,000 pounds.
- Each box weighs 40 pounds.
The total weight when the truck is loaded with boxes is given by: \[ \text{Total Weight} = \text{Weight of Truck} + \text{Weight of Boxes} = 40,000 + 40b \]
Since the bridge can hold a maximum of 75,000 pounds, we set up the inequality: \[ 40,000 + 40b \leq 75,000 \]
Now, we will solve for \( b \):
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Subtract 40,000 from both sides: \[ 40b \leq 75,000 - 40,000 \] \[ 40b \leq 35,000 \]
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Divide both sides by 40: \[ b \leq \frac{35,000}{40} \] \[ b \leq 875 \]
Thus, the maximum number of boxes \( b \) that the truck can carry to cross the bridge is given by the inequality: \[ 0 \leq b \leq 875 \] (assuming \( b \) cannot be negative).
So, the final answer is: \[ 0 \leq b \leq 875 \]