If you want to try to solve this problem in "words" rather than forming and solving equations then you could adopt this approach:-
After James had made 3 cakes there was [imath]\bf\small\frac{3}{4}[/imath] of the packet of flour left. This means that he must have used [imath]\bf\small\frac{1}{4}[/imath] of the packet to make those 3 cakes ([imath]\bf\small\frac{4}{4}[/imath] - [imath]\bf\small\frac{3}{4}[/imath] = [imath]\bf\small\frac{1}{4}[/imath]) and, therefore, he is using [imath]\bf\small\frac{1}{12}[/imath] of the packet for each cake ([imath]\bf\small\frac{1}{4}[/imath] divided by 3).
(NB: [imath]\bf\small\frac{4}{4}[/imath] and [imath]\bf\small\frac{12}{12}[/imath] are both ways to represent the whole packet flour; you do see that don't you?)
Therefore, after he has made another 5 cakes (3 + 5 = 8 cakes in total) he will have used [imath]\bf\small\frac{8}{12}[/imath] of the packet of flour (8 × [imath]\bf\small\frac{1}{12}[/imath] = [imath]\bf\small\frac{8}{12}[/imath]).
This means that he has [imath]\bf\small\frac{4}{12}[/imath] of the packet left ([imath]\bf\small\frac{12}{12}[/imath] - [imath]\bf\small\frac{8}{12}[/imath] = [imath]\bf\small\frac{4}{12}[/imath]).
So the 1,400 g of flour that remain after he has baked his 8 cakes is actually [imath]\bf\small\frac{4}{12}[/imath] (or [imath]\bf\small\frac{1}{3}[/imath]) of the whole packet.
Can you now work out how much flour James was using to make each cake?
(Hint: He now has enough left ([imath]\bf\small\frac{4}{12}[/imath]) to make another four cakes, doesn't he? ?)
Please come back and tell us your answer (and show us your working too, please).
Hope that helps. ?