v1 is the speed of car 1 (in km/h), x1 is the distance that car 1 travels (in km). Similar for car 2
One car's speed is 10 kilometers per hour less than the other's, that is,
[tex]v_1=v_2-10[/tex]Speed is defined as distance divided by time, then
[tex]\begin{gathered} \frac{x_1}{t}=\frac{x_2}{t}-10 \\ t\cdot\frac{x_1}{t}=t(\frac{x_2}{t}-10) \\ x_1=x_2-10t \end{gathered}[/tex]If they meet in 4 hours, then t = 4. Also, x1 + x2 must be equal to 760 km.
[tex]\begin{gathered} x_1=x_2-10\cdot4 \\ x_1=x_2-40 \\ \\ x_1+x_2=760 \\ x_2-40+x_2=760 \\ 2x_2=760+40 \\ x_2=\frac{800}{2} \\ x_2=400 \\ \\ x_1=400-40\text{ = 360} \end{gathered}[/tex]Finally, the speed of the slower car is:
[tex]\begin{gathered} v_1=\frac{x_1}{t}_{} \\ v_1=\frac{360}{4}_{} \\ v_1=90\frac{\operatorname{km}}{h} \end{gathered}[/tex]
