4. A car starts from the point \(A\). At time \(t \mathrm {~s}\) after leaving \(A\), the distance of the car from \(A\) is \(s \mathrm {~m}\), where \(s = 30 t - 0.4 t ^ { 2 } , 0 \leqslant t \leqslant 25\). The car reaches the point \(B\) when \(t = 25\).
a Find the distance \(A B\).
b Show that the car travels with a constant acceleration and state the value of this acceleration. A runner passes through \(B\) when \(t = 0\) with an initial velocity of \(2 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) running directly towards \(A\). The runner has a constant acceleration of \(0.1 \mathrm {~m} \mathrm {~s} ^ { - 2 }\).
c Find the distance from \(A\) at which the runner and the car pass one another.
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