Solve all questions in this paper

The variable $y$ is partly constant and partly varies as $x$. This can be expressed as $y = c + kx$, where $c$ is the constant part and $k$ is the constant of variation.

When $x=2, y=7$:

When $x=5, y=13$:

Subtract equation $(*)$ from equation $(**)$:

Substitute $k=2$ into equation $(*)$:

Substitute the values of $c$ and $k$ back into the general equation:

*a) The expression for $y$ in terms of $x$ is $\boxed{\mathbf{y = 3 + 2x}}$.

Substitute $x=10$ into the equation $y = 3 + 2x$:

*b) The value of $y$ when $x=10$ is $\boxed{\mathbf{23}}$.