100 because sum means addition so 1+0+0 is one, and one X one hundred is 100
Hope this helps :D

with y equaling the total and x equaling the number if months
You have -4,-3,-2, that is a 3 out of a total of 21 points or numbers on the number line. 3/21 is reduces to 1/7.
3 goes into 21 , 7 times. That is why it reduces to 1/7.
12,500 / 100 = 125 125 x 4.5 = 562.5 562.5 x 4 = 2250
2250 + 12,500 = 14,750 He paid back a total of $14,750. Hope this helps :)
4x+2y i hope that helps :3