F.2 maths``plz help&fast!!

A+B = 48+72 = 120books

of the no. of A's books to that of B becomes 13:17 (呢度有書30份,A分到13份,B分到17分,所以每份有書

120/(13+17) = 4

A有13份而每份係4本書,所以A有4x13 = 52

本來A有48本 但而家係52本,所以52-48 = 4

The no. of books that A borrowed from B is 4

let A has borrows x books from B.
(48+x)/(72-x)=13:17
816+17x=936-13x
30x=120
x=4
So, A has borrows 4 books from B

A向B借X本書
借書後A有48+X本書
B有72-X本書

(48+X):(72-X)=13:17
13*(72-X)=17*(48+X)
936-13X=816+17X
X=4

設A借了B有x本書
(48+x)/(72-x)=13/17
816+17x=936-13x
30x=120
x=4
So, B borrows 4 books to A