$A$, $B$ and $C$ are three points on a line of greatest slope of a smooth plane inclined at an angle of ${\theta ^ \circ }$ to the horizontal. $A$ is higher than $B$ and $B$ is higher than $C$, and the distances $AB$ and $BC$ are $1.76{\text{ }}m$ and $2.16{\text{ }}m$ respectively. A particle slides down the plane with constant acceleration $\alpha m{\text{ }}{s^{ - 2}}$. The speed of the particle at $A$ is $um{\text{ }}{s^{ - 1}}$ (see diagram). The particle takes $0.8{\text{ }}s$ to travel from $A$ to $B$ and takes $1.4{\text{ }}s$ to travel from $A$ to $C$. Find

a) the values of $u$ and $\alpha $,

b) the value of $\theta $.