The formula
lines = 2 to the power of the doubles × 3 to the power of the trebles
Where it comes from
Every match marked as a double multiplies the number of lines by two, and every treble multiplies it by three. Because the factors multiply against each other the count grows exponentially: four doubles and two trebles is already 144 lines, and eight doubles with four trebles passes twenty thousand.
How to work it out by hand
- Count the matches marked as doubles and raise two to that power
- Do the same with the trebles as a power of three
- Multiply the two results together
- Multiply by the price of a line
What is worth knowing
It is worth keeping the scale in mind: fourteen matches on three results each give 4,782,969 possible combinations. A coupon of 144 lines covers 0.003 % of them. Multiples do not improve your chance per unit spent, they only concentrate the spending on the results you think most likely, which is a judgement call rather than a mathematical one.