A train fare cost £23.55 all train fares are increased by 2.8% work out the new fare

Whatever% of anything is just (whatever/100) * anything.

if the old fare of 23.55 was the 100%, and it got increased by 2.8%, then the new fare is 100% + 2.8% or 102.8%.

how much is 102.8% of 23.55? well is just (102.8/100) * 23.55.