A company that makes bicycles has determined that a new employee can assemble $M(d),$ where $M(d)=\frac{105d^2}{2d^2+7},$ bicycles per day after $d$ days of on$-$the$-$job training.

a$.$ Find the rate of change function for the number of bicycles assembled with respect to time.

b$.$ Find and interpret $M^{\text{'}}(2)$ and $M^{\text{'}}(5).$

The rate of change function for the number of bicycles assembled with respect to time is $M^{\text{'}}(d)=$