Mr. Chambliss is planning to build a shed with a rectangular floor. In his original plan, the length of the floor was 7 feet and the area of the floor was 35 square feet. In his new plan he wants to extend the length by 3 more feet. If the total area of the shed will be 70 square feet, by how many feet will he have to extend the width?
A. 1 foot
B. 2 feet
C. 3 feet
D. 4 feet