Heather purchased a prepaid phone card for $30 . Long distance calls cost 14 cents a minute using this card. Heather used her card only once to make a long distance call. If the remaining credit on her card is $28.18 , how many minutes did her call last?

30- 28.18= 1.82 (original amount minus the amount remaining)

1.82/0.14= 13 (how much was spent off the card divided by how much each minute costs)

she was on the call for 13 minutes

The questions seems incomplete, so I will answer it in a general way. I suppose you have a table with the average monthly rainfall for each month (from January to December). To compute the sum of them just add together all of the average monthly rainfall.

For the case of the table attached, the sum is:

7.57 + 9.6 + 28.45 + 73.8 + 141. 31 + 267.6 + 314 + 275.1 + 336.47 + 171. 71 + 15.3 + 3.94 = 1644.85 mm