To determine the maximum number of boxes \( b \) that the truck can carry while crossing the bridge, we can set up the following inequality:
- The weight of the truck is 40,000 pounds.
- Each box weighs 40 pounds.
- The maximum weight the bridge can hold is 75,000 pounds.
The total weight of the truck plus the boxes can be expressed as:
\[ 40,000 + 40b \]
where \( b \) is the number of boxes. To ensure that the total weight does not exceed the bridge's maximum capacity, we set up the inequality:
\[ 40,000 + 40b \leq 75,000 \]
Now, we can solve for \( b \):
- Subtract 40,000 from both sides:
\[ 40b \leq 75,000 - 40,000 \]
\[ 40b \leq 35,000 \]
- Divide both sides by 40:
\[ b \leq \frac{35,000}{40} \]
\[ b \leq 875 \]
Thus, the maximum number of boxes the truck can carry to cross the bridge is represented by the inequality:
\[ b \leq 875 \]
In summary: \[ b \leq 875 \]