Clifford is an engineer earning $69,600 a year and his wife Bonita is a sales manager earning $86,400. In discussions with their insurance agent, the couple decide that if either of them were to become disabled, they would be able to live off a combined income of $9,000 a month. How much disability coverage does the couple require for Clifford in order to meet the couple's goals?

a) $1,800

b) $3,200

c) $3,480

d) $7,800