$$ Cyclists A and $B$ are moving on the road with speeds of $7$

$\frac{m}{s}$ and $8\mathrm{.}5\frac{m}{s}$ as shown. At the same time, riders A and $B$

are traveling at speeds of $0\mathrm{.}5\frac{m}{s^{{?}^{{?}^{?}}}}2$ and $0\mathrm{.}7\frac{m}{s^{{?}^{{?}^{?}}}}2$

respectively. They start to accelerate with, relative to $B,$ the

bike A speed and determine its acceleration.