[单选题]
An object is 15 mm in front 7aof x:gyyua 6mn)m5es k(rp w//48ce of a converging lens, and b ,.rxbo pu;43hiz4r fthe image is 4.0 mm behind4.f4 o bhxuri3,zp;br the lens. What is the focal length of the lens?
A. $11 \; mm$
B. $5.5 \; mm$
C. $3.8 \; mm$
D. $3.2 \; mm$
