Multiply the values of a and c together;
9*30= 270 <— find prime factors of this
270= 3*3*3*5*2
Now find a way to add these factors in different ways to give 33 (b value)
We can try (3*3*2)+(3*5)=?
18+15=33
Now that you know the numbers, break down the b value.
9x^2+18x+15x+30
9x(x+2)+15(x+2) <— make sure the brackets are the same
(9x+15)(x+2) <— check if this expands to the initial answer
Hope I helped :)