there is also other way of understanding this:
Identify who is better off in the spot market, opposite party to him bears the credit risk
for a) Current price = 100 PV of frwrd = 102.84
so long party is better off in the spot market (i.e. his stock whose CMP is only 100 but he has agreed to pay for this by going long at 102.84 - so he would happy in the spot market if not got long in the frwrd market) - Opposite party (i.e. short party) will bear the credit risk.
for B) & C) long is getting the stock cheaper in frwrd market than the spot market so short party is better off in spot market. Opposite party to short (i.e. long party) bears the credit risk
Another way to understand -
Look out for the one who can make money by closing frwrd contract & doing transaction in spot market
i…e CMP 100 PV of frwrd 102.84
short party will close the frwrd at 102.84 to long & will buy the stock in spot only for $ 100. He will gain $2.84 so he bears the credit risk if long party defaults & shows his unableness to honor the obligation for buying stock at agreed frwrd rate.
for B & C - long party can make gain by closing frwrd contract & seling the stock in spot. So he bears the credit risk