Final answer:
The mechanical advantage of the forklift is 4, as it multiplies the input force by this amount to lift a crate that requires 900 newtons with an input force of 225 newtons.
Step-by-step explanation:
The mechanical advantage (MA) of a machine indicates how much the machine can multiply the input force to perform work. In the case of the forklift mentioned, we calculate the MA using the formula MA = output force / input force. Given that the crate required 900 newtons (N) of force to lift and the forklift's engine provided 225 N of force, the mechanical advantage of the forklift is 4 (900 N / 225 N).