Question 15.

We can use the formula for when two people moving towards each other and meeting in a straight line. $t^2=t_1\times\ t_2$

Where $t$ is time taken for them to meet each other. $t_1$ is the time taken by person 1 to reach the destination after meeting and 

$t_2$ is the time taken by person 2 to reach the destination after meeting

We are told they meet each other in 1 and a half hours, that is 90 minutes. 

And if Sunil takes X minutes to reach A, Anil will take X+75 minutes

Since it is given that, Anil reaches B exactly 1 hour 15 minutes after Sunil reaches A

$90^2=x\left(x+75\right)$

$8100=x^2+75x$

$x^2+75x-8100=0$

$\dfrac{\left(-75\pm\sqrt{5625+32400}\right)}{2}$

$\dfrac{\left(-75+195\right)}{2}$

$x=60$

Total time of travel of Anil is, $90\ \min\ +60\ \min\ +75\ \min$

Total of 225 minutes. 

Time in hours will be 3.75 hours. 

Speed is $\dfrac{45}{3.75}=12\ \dfrac{km}{hr}$