How many solutions are there to the equation x1 + x2 + x3 + x4 + x5 + x6 = 25 in which each xi is a non-negative integer and …

(a)there are no other restrictions.

(b) xi ≥ 3 for i = 1, 2, 3, 4, 5, 6

(c) 3 ≤ x1 ≤ 10

(d) 3 ≤ x1 ≤ 10 and 2 ≤ x2 ≤ 7

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.