Co-ordinates of O - (0, 0) [Taken this as an assumption, but unless defined otherwise, O is usually taken to be the point of origin on the Cartesian plane]
Co-ordinates of P - (x1, y1), y = 4x+3
When x = x1, y = 4x1+3, hence y1 = 4x1+3
Therefore co-ordinates of M (midpoint of OP) is...