10. The straight line \(l\) has gradient 3 and passes through the point \(A ( - 6,4 )\).
- Find an equation for \(l\) in the form \(y = m x + c\).
The straight line \(m\) has the equation \(x - 7 y + 14 = 0\).
Given that \(m\) crosses the \(y\)-axis at the point \(B\) and intersects \(l\) at the point \(C\), - find the coordinates of \(B\) and \(C\),
- show that \(\angle B A C = 90 ^ { \circ }\),
- find the area of triangle \(A B C\).