It took me along time to understand it too heather but the answer is 25.
I will try and explain -
on final row...each damper(spark plug) ) =2, so multiply 2 by one piston (which = 20 as they are 10 each) plus the one tyre which is 5, so total =25.
Yes it only shows one damper(spark plug but the value of that is 2 and you use that value to multiply)
The value one on on it's own is 2, so in the row where there are 2 their totals =4 plus the value of one tyre which is 5 so that row then totals 9.
In the last row you have one which we know it's value is 2, so you use its value to multiply it by the piston and then add the tyre value of 5.