thoi oto di den B la t: (h)(t>0)
van toc la 120/t
thoi gian xe may den B : t+5/4
van toc xe may la : 120/(t+5/4)
pt
120/(t+5/4)+10=120/t
gpt
<=>12t+t(t+5/4)=12(t+5/4)
<=>t^2+5t/4-15=0
∆=25/16+60=985/16
t=(-5+√985)/8~3,3(h)=3(h)18'
ket luan
oto den b luc 10(h)18'

giai linh tinh.

5/4 ở đâu ra v?