Jan visits Fat Lizard, a restaurant in Otaniemi, with his two friends. They buy a cheesy pepperoni pizza, a big fat spicy pizza, and three cokes. The total is 51,50 €. Jan pays this with his credit card, and both of his friends paid him 11,00 €.

a) How much did a bottle of coke cost?
b) Did Jan's friends pay him the correct amount, too much, or too little, given that Jan ate the Big Fat Pizza?

The menu can be found at: https://ravintolafatlizard.fi/ruoka/