No, because 7 x 21 is 147.
it would obviously take 15 days if this answers your question
(a) need to find the number of books, we'll call it "b". then the money (6w) minus the cost of books (17b) equals change left over (w)
6w - 17b = w
6w - w = 17b
5w = 17b
(5/17)w = b
(b) if w = 34
(5/17) *34 = b
10 = b
1/4(2x-14)=4
2x/4-14/4
X/2-7/2=4
x-7/2=4
8=x-7
8+7=x
X=15
