Christi alters a skirt. she cuts 7 inches off the bottom of the skirt and then adds

Christi alters a skirt. she cuts 7 inches off the bottom of the skirt and then adds a 5-inch ruffle to the skirt's remaining bottom edge. which expression best represents the final length of the skirt?

a. 2-s

b. 2+s

c. s-2

d. s-12

evan chose d as the correct answer. how did he get that answer?