Equation for two lines that intersect at infinitely many points. Please?

The multiplication property of zero states that the product of any number and 0 is 0. what must be true about either a or b to make ab=0

Dean and karlene get paid to write songs. dean is paid a one-time fee of $20 plus $80 per day. karlene is paid a one-time fee of $25 plus $100 per day. write an expression to represent how much a producer will pay to hire both to work the same number of days on a song.

*let m∠cob = 50°30’, m∠aob = 70° and m∠aoc = 20°30’. could point c be in the interior of ∠aob? why?