Question 67919
255/x=255/(x+10)+.4
255/x=(255+.4x+4)/(x+10)
255/x=(259+.4x)/(x=10)
255(x+100=x(259+.4x)/(x+10)
255x+2550=259x+.4x^2
.4x^2+4x-2550=0
(.4x-30)(x+85)=0
.4x-30=0
.4x=30
x=30/.4
x=75 km/h is the normal speed
75+10=85 km/h is the faster trip speed
proof
255/75=255/85+.4
3.4+3+.4
3.4=3.4