Problems-solving in Equations The distance between the two cities A and B is 300 km, set off a car from the city a toward the city b by speed 90 km/h and set off from the city b bicycle toward a by speed of 10km/h.  if you knew that the car and the bike were based in nine in the morning. Select the time that the car and the bike are going to met ?      
Equation for the 8th grade ! 
Please help i need to get a formulation of this equation 

Here are two ways of tackling this:
1)
Let $e_1$ be the distance traveled by the car in $t_1$ hours.
Let $e_2$ be the distance traveled by the bike in $t_2$ hours.
When the car and the bike meet, the will have been traveling for the same amount of time (since they set off at the the same time). Then, $t_1=t_2$.
$$e_1+e_2=300km$$
$$v_{car} \, t_1 +  v_{bike} \, t_2 = 300km$$
$$90\frac{km}{h} \, t_1 +10\frac{km}{h} \, t_1  = 300km$$
$$100\frac{km}{h} \, t_1 =300km$$
$$t_1=3h$$
2) Notice that the distance between the car and the bike gets shortened by $100 \frac{km}{h}$ and you get again $100 \frac{km}{h} \, t = 300km$.
If they set off at nine, they will meet at twelve.
