Hello!
This is just a conceptual problem where you'll be converting units.
If her semitrailer is 3.5m high and the bottom of the bridge (how tall the support beam are) is 11ft 9in high, we'll need to convert them into the same units and then compare both values.
Let's convert from inches to meters.
Since there are 12 inches in a feet, we can convert 11 feet into 132 inches, meaning that the bottom of the bridge is at 141 inches.
In 1 meter, there is around 39.37 inches, so we'll be dividing 141 by 39.37, giving us a number of around 3.5814, meaning that the bottom of the bridge is higher than the height of the semitrailer, and her vehicle will fit under the bridge.
Hope this helps!