In the figure if PQ parallel to RS then find the relationship between a ,b,c

Question

Description of figure - draw two parallel lines PQ and below RS .leave a small gap between the lines .then mark a point O which Is equal distance on either side of line .draw a shape of capital V from point O which cut PQ LINE at point M and cut RS line at N .then MARK angle  PMO=a ,angle MON = b, angle ONS = c.then solve it ....cud y please help me 

Answer 1

Extend MO so it crosses RS. m∠ QMO = 180-a because it forms a supplementary angle with a. m<OSN = 180 -a  because parallel lines yield congruent alternate interior angles.

For ΔOSN, b is an exterior angle for the two remote interior angles, ∠ONS and ∠OSN.

That means b = 180 - a + c