30 cans in total. 60% coke, 40% pepsi.

that means 18 cans is coke and 12 cans is pepsi.

After drinking some amount of cans of coke, now 25% is coke and 75% is pepsi.

the remaining amount has to be divisible by 4, so trying is probably faster than using equations.

if remaining 28, coke 16- no good

if remaining 24, coke 12- no good

remaining 20, coke 8- no good, but close

remaining 16, coke 4- that's our answer, and that means Noah drink 14 cans of coke.