Card B: 80 ÷ [(80+20) ÷ 0.35] = 80 ÷ (100×100/35) = 80× 35 ÷100 ÷.
So 0.291667-0.28 = 0.011667 ≈ 0.01is a penny.
A: One card is cheap, about 1 cent per minute.