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.