Maths modelling question

Please could someone help me with part f of this question, it is only worth one mark but I'm not sure how to approach it

Youve got "the" answer, so multiply the cos term by a decaying exponential (or similar) so that term tends to zero and P converges to 5000.

When you solve (2nd order) linear odes, one class of solutions is an exponential multiplied by a sinusoid. This question part is alluding to that.