a)[tex] \frac{d2}{d1} = 0,5 \\
\frac{d2+d1}{2} = 66 km \\
\frac{v2*t + v1*t}{2} = 66 km \\
\frac{25km/h * t + 30km/h * t}{2} = 66km \\
\frac{t(25km/h + 30 km/h)}{2} = 66km \\
\frac{t * 55}{2} = 66km\\
t * 55= 132\\
t = 2,4h[/tex]
b) [tex]v1 * t1 = d \\
v2 * t2 = d \\
t2 - t1 = 1h \\
t2 = t1+ 1h \\
v1 * t1 = v2 * t2 = d \\
30km/h * t1 = 25km/h * (t1+1h) \\
30t1 = 25t1 + 25\\
5t1 = 25\\
t1 = 25/5 \\
t1 = 5h\\
d = 30km/h * 5h = 150km\\
[/tex]