Three survey markers are meant to lie on one straight line…

Step 1. The ratio from $x$. $\lambda = \dfrac{x_B - x_A}{x_C - x_B} = \dfrac{3 - 1}{7 - 3} = \dfrac{1}{2}$.

Step 2. The coordinate $p$. $\lambda = \dfrac{p - (-2)}{10 - p} = \dfrac{1}{2}$, so $2(p + 2) = 10 - p$ and $3p = 6$. So $p = 2$.

Step 3. The coordinate $q$. $\lambda = \dfrac{7 - 3}{q - 7} = \dfrac{1}{2}$, so $q - 7 = 8$ and $q = 15$.

Step 4. The ratio. $B$ divides $AC$ in the ratio $1 : 2$, and $\dfrac{m}{n} = 0.5$.