05 - Two runners moving in opposite directions in a circular track

Rate of Benjie
$v_B = \dfrac{400}{65} = \dfrac{80}{13}$
 

Rate of Jerwin
$v_J = \dfrac{400}{t}$
 

Benjie and Jerwin run a total of 400 m in 35 seconds
$s_B + s_J = 400$

$\left( \dfrac{80}{13} \right)(35) + \left( \dfrac{400}{t} \right)(35) = 400$

$\dfrac{7}{13} + \dfrac{35}{t} = 1$

$\dfrac{35}{t} = \dfrac{6}{13}$

$t = 75.83 ~ \text{sec}$           answer