Draw both for a $20 strike: the call zero below the strike then slope 1 above it, the put its mirror with slope −1, capped at the strike when the stock reaches zero.
2
Net payoff and the break-even point
Shift the gross payoff down by the premium, write net payoff as gross payoff minus premium with interest ignored, and locate break-even at K+C for a call and K−P for a put.
3
Returns on a call versus the stock
Sketch both return lines, recording the call's return of −100% until the stock clears strike plus premium, and note non-linearity as what sets credit default swap portfolios apart from stocks and bonds.