23.
f(x) is just a function in terms of x.
where it says 4f(2) all that means is 4 times the function when x is 2.
To work it out, you just need to swap all xs with 2 and calculate what that is. That gives you f(2), then multiply that answer by 4 to get 4f(2)
Same thing for g(x). First step swap xs for 6 to get g(6) then multiply answer to get 6g(6). At that point, you should have 2 numbers with no x's and you can minus the f by g.
24. Is about compound interest which means that after each year a new amount is worked out rather than a flat amount for the whole 8 years.
2 ways to tackle it, you could work out 8% of each year but that would require you to work it out 8 times which is time consuming and possible to make errors.
2nd way is much easier in that regard.
Final Answer = Initial Amount * (1 + interest rate)^amount of years.
Answer = 5000*(1+0.08)^8