Peter buys tunа аnd gоlf bаlls. The price оf tuna is $2 a can, and the price оf golf balls is $1 each. Each month, Peter spends all his income and buys 20 cans of tuna and 40 golf balls. Next month, the price of tuna will rise to $3 a can and the price of golf balls will fall to $0.5 each. Which of the following statements is correct?