Alice and the Hatter play a game. Alice takes a coin in each hand: 2p coin and 5p coin, one coin per hand. Then she multiplies the value of the coin in the left hand by 4, 10, 12, or 26, and the value of the coin in the right hand by 7, 13, 21, or 35. Finally, she adds the two products together, and tells the result to the Hatter. To her surprise, the Hatter immediately knows in which hand she has the 2p coin. How does he do it?