How do i turn factions to decimals?

Such as 2/7 written as a decimal is:

Adeposit of 5500 at 6% for 3 years equals

1. according to the internal revenue service, the mean tax refund for the year 2007 was $2,708. assume the standard deviation is $650 and that the amounts refunded follow a normal probability distribution. a. what percent of the refunds are more than $3,000? b. what percent of the refunds are more than $3,000 but less than $4,000? c. what percent of the refunds are less than $2,000?

Ineed with question three. i don't understand how i'm supposed to achieve 3 marks.