A gardener is preparing 7 flower beds. Each bed will have either rose bushes or tulip bulbs, but not both. Rose bushes require 9 pounds of soil, and tulip bulbs require 2 pounds of soil. If $x$ is the number of beds that will be set up for rose bushes and the remaining beds will be set up for tulip bulbs, which of the following expressions represents the total number of pounds of soil required?