Let me do the maths if you want to get first class.
Using the previous calculations, if you want to get 1st class, the
minimum value you shall get for X is
4.50 x (40 - 3) = 4.50 x 37 = 166.5
So, you have 166.5 - 120 = 46.5 for your 4 modules and honours
project (or equivalently 8 modules) to get. (Sorry for the bad
phrasing)
But then we see that 46.5 / 8 = 5.8125 > 5 = A/A+ grade
So, to conclude, 1st class is impossible for you now. Dun worry
lah, 2nd upper is pretty good already. 
