Calculating bounds of an expression

I've been stuck on this question and don't understand how the answer is worked out:
$E = mc^2 c = 3.0 x 10^8 (2 s.f.) m= 2.4 (2 s.f.)$
Calculate lower bound of E. Calculate upper bound of E.
The answer is $2.05 x 10^17 (3 s.f.) (LB) and 2.28 x 10^17 (3 s.f.) (UB)$

Question, for c is the LB & UB worked out for each number (3.0 and 10^8) or do you workout each number individual. e.g. LB is 2.95 & 9.5^8

My answer was incorrect by quite a bit. I would be grateful if someone can show how they get to the answer as i'm lost.