Mechanical advantage is the ratio of output force to input force. In this case, the output force is 10 newtons, and the input force is 2.5 newtons, so the mechanical advantage is:

$$MA = \frac{Output\space Force}{Input\space Force}$$

$$MA = \frac{10N}{2.5N}$$

$$MA = 4$$

Therefore, the mechanical advantage of this system is 4, which means that the output force is 4 times greater than the input force.