2.4 + 5.4q – 4.5q + 3.6 a.6+1.1q b.9.9q+6 c.0.9q+6 d.9.9q-6

You have to add the same kind of terms, in this case the ones that have a variable (5.4q and -4.5q) and the ones that don't (2.4 and 3.6), like this:

(5.4q - 4.5q) + (2.4 + 3.6) = 0.9q + 6

The answer is c. 0.9 +6