Final answer:
Erik wins the game when the difference is less than 10. Nita's number is 12.
Step-by-step explanation:
To determine who wins, we need to calculate the difference between Erik's number and Nita's number. If the difference is less than 10, Erik wins. If the difference is greater than 10, Nita wins.
a) If Erik selects 4 and Nita selects 12, the difference is 12 - 4 = 8. Since the difference is less than 10, Erik wins.
b) To find out what number Nita picked, we can add the difference to Erik's number. Since the difference is 8 and Erik picked 4, Nita must have picked 4 + 8 = 12.