>>14195623way 1, sum:
-60 + 70 - 80 + 90 = -140 + 160 = 20
he made $20
way 2, for the retards, literally give him a starting amount and go through the motions:
man has $200
buys goat for $60, now man has $140
sells goat for $70, now man has $210
buys goat for $80, now man has $130
sells goat for $90, now man has $220
man had $200, now he has $220
man made $20
Q.E.D
