Re-read the preamble, there's plenty of instruction there.
It may even help if you ignore the fact that this has anything to do with betting, and just view it as three (win/each way place/each way win = rule 1, rule 2, rule 3) basic mathematical rules for solving equations.
Hence, for 1 across, Agio 70p win you are looking at Rule 1 which is that at 1 to 1 the return is 1x70p +70p at 2 to 1 the return is 2x70p + 70p and so on. You may well therefore need to work out the return for all items from 1 to 1 to 100 to 1 for each possible bet.
Rule for place only simply says divide the odds (1 to 10) by 4 and do the same math.
Rule for each way win says first do the win math, then with the other bet do the place bet and then add the two parts.
Sorry I'm no maths teacher, but you only need to understand and apply these 3 simple rules.
The hard bit is applying these rules to a range of odds from 1 to 100 to one, hence your first calculations pre-elimination are manifold ... .
A spreadsheet helps if you can muster an electronic version.
Good Luck