math
posted by Jaz .
can u please help me with this math problem. i don't get how to do this question.
Mrs. Mabie has a rectangle swimming pool that measures 25 feet by 14 feet. She wants to have a cement walkway installed around the perimeter of the pool. The combined area of the pool and walkway will be 672 square feet. What will be the width of the walkway?

let the width of the walkway be x ft
dimensions of the whole thing = (25+2x) by (14+2x)
(25+2x)(14+2x) = 672
350 + 78x + 4x^2  672=0
4x^2 + 78x  322 = 0
x = (78 ± √11236)/8
= 3.5 or a negative
the width should be 3.5 ft
check:
length = 25+7 = 32
width = 14 + 7 = 21
32 x 21 = 672