the cost of building lawn xmetre long varies partly as x and partly as xsquare.The lawn cost #180 if it 30metre long and #280 if it 40metre.How long is a lawn if it cost #4000 to build.

Answer 1

c = hx + kx^2

180 = 30h + 900k
280 = 40h + 1600k
h = 3
k = .1

c = 3x + .1x^2

4000 = 3x + .1x^2
x = 185.5