Answer
$m=13.35 ~lb$
Work Step by Step
It is given that the spring deflects 0.14 in. for the applied force of every 1 lbf. So, the stiffness of the spring is
$k=F/δ=1/0.14=7.143~ lbf/in.$
This force is equal to the weight of the object (W).
$W=k×δ=7.143×1.8=12.857 ~lbf$
The mass of the object is
$m=W/g=12.857/31×32.2$
$m=13.35 lb$
