CAT4MBA

hey der ans is simple

for triangle u need 3 points but for that u have to select 2 pints from 1 line and another 1 point from anoter line

so

for case (1) u select 2 points from AB line and 1 point from AC line
or 2 points from AC line and 1 point from AB line

so ans is mC2 * nC1+mC1*nC2

for second case

u have 1 more point A

so m+1c2 x nC1 but here u cant take n+1c2 x mC1 because A point already taken in m+1C2

so ans is m+1C2*nC1+mC1*nC2

so final ans option(3)

LIttle Star