Which of the following is equivalent to 3a + 4b – (–6a – 3b) ?
a. 16ab
b. –3a + b
c. –3a + 7b
d. 9a + b
e. 9a + 7b

6. sarah saved $12.75 every week for a number of weeks, w. she received an additional $25 during the last week in which she saved money. write and solve an equation to find the number of weeks, w, for which sarah had saved money if she has $114.25 now.