Measure any distance along the river bank
We will pretend
it is 40 metres.
A to C = 40 metres
Measure any distance perpendicularly from C to D.
We will pretend it is 12 metres.
C to D = 12 metres
From point D imagine a straight line to B.
Notice the intersection point E.
Measure the distance from E to A
A to E = 24 metres.
E to C is 16 metres.
Now apply this math formula- AB:DC = AE:EC
Therefore the width of the river is 18 metres.
= 18 metres