Ok,

got it to work

If the goal is to make 25 units profit
when;

TAB 1: DIVS - 3.50, UNITS TO BET: 13
TAB 2: DIVS - 4.00, UNITS TO BET: 11
TAB 3: DIVS - 5.00, UNITS TO BET: 9

TOTAL BET UNITS: 33

TAB 1, if it won, 13 units * 3.50 = 45.50 rtn - 33 cost = 12.50 profit.

TAB 2, if it won, 11 units * 4.00 = 44.00 rtn - 33 cost = 11.00 profit.

TAB 3, if it won, 13 units * 5.00 = 65.00 rtn - 33 cost = 32.00 profit.

Of course this is above the 80% rule, but the point is how does it arrive at those bet unit amounts,

what's the formula ?

Example 2
If it's set to make 100 units profit using the same DIVS

1: 52 units. DIVS - 3.50. 182 rtn - 134 = 48 profit
2: 46 units. DIVS - 4.00. 184 rtn - 134 = 50 "
3: 36 units. DIVS - 5.00. 180 rtn - 134 = 46 "

Total cost: 134

Thanks