Answer:
Infinite series equals 4/5
Step-by-step explanation:
Notice that the series can be written as a combination of two geometric series, that can be found independently:

The first one:
is a geometric sequence of first term (
) "1" and common ratio (r) "
", so since the common ratio is smaller than one, we can find an answer for the infinite addition of its terms, given by: 
The second one:
is a geometric sequence of first term "1", and common ratio (r) "
". Again, since the common ratio is smaller than one, we can find its infinite sum:

now we simply combine the results making sure we do the indicated difference: Infinite total sum= 
6.25
explanation: if you divide 6.25 by 5 you get 1.25, if you divide 17.40 by 12 it’s 1.45. Therefore you pay more.
For 3 it’s b. For 2 it’s 8. For 4 it’s the whole number