It requires yet another mean formula that's not listed here (you'll need to assume something).

As it is, it's still unsolved so do head over there and try it if you can

As you can see this is a set of grouped data, so we cannot use the first formula to calculate your mean.

Since the mean is now , we get

Solving the above you'll get x = 6.

Once again Miss Loi can't emphasize enough the importance of knowing which row in the table refers to your x (the number of hours in this case) and which refers to your frequency (the number of students in this case). Which is probably what led to your careless mistake in your earlier comment

Also many students get confused about the Σf in the bottom of the equation. They ended up (in this example) adding up 0+1+2+3+4 or simply dividing the whole expression by 5!