All breakpoints are exactly located a Grid

The two lateral, highest points $($bank$-$floodplain breakpoints$)$ are at the same elevation

Bankfull width is $16m$

Bankfuil depth is $6m$

The two middle points $($channel bed$)$ are strictly below floodplain, and at different elevations

No horizontal bed, no rectangular sections, no regular triangles, no isosceles triangles, no ${45}^{\text{@}\text{'}}$ lines, nothing symmetrical $($just your own random choice of two points$)$

a$.)$ Derive mathematical expressions for $A(y),b(y).$ and $P(y),$ for $y$ ranging from $0$ to bankfull depth.