You need to give more info.
First you need to put everything as 1 unit. I'll convert both to fractions for now.
75% = 3/4
680/1 * 3/4
Cross Multiply
2040/4
Simplify
510
The mayor received 510 votes.
Olivia's sample space consists of 36 pairs. Three (3) of them give a total of 10: (4, 6), (5, 5), (6, 4).
The probability of getting a total of 10 is 3/36 = 1/12.