Tricky Trapezium

Level pending

ABCD is a trapezium (UK) / trapezoid (US) in which AD=BC, AB and DC are parallel, and the diagonals AC and BD intersect at O. Given that OA=(2x+1) cm, OB=(5x-3) cm, OC=(6x-5) cm and OD=(3x-1)cm where x is a real number, the ratio of areas$\frac{OCD}{OAD}$ can be expressed as a fraction $\frac{a}{b}$ in simplest form where a and b are coprime integers. Find a+b.

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