LF is lift / weight, or n=L/W. All other factors being equal lift and weight can be expressed as changes of Cl for the purpose of the calculation. Weight does not change, and so the Cl required is the same after the event as before (when considering the calculation). However lift increases as per the conditions in the question. In this case it increases by 3 x 0.1 =0.3. So for the calculation the Cl after the event is 0.42+0.3=0.72. Divide this by the original Cl to get the answer.

Mathematically it looks like:
(0.42+(3x0.1)) / 0.42.

Beware some questions ask for the change of load factor, in which case you have to subtract the original LF from the new one.