Data regarding Ball Corp.$$s investment in available$-$for$-$sale debt securities follow:

Cost Fair Value

December $31,$ Year $3$ $$150,000$ $$130,000$

December $31,$ Year $4150,000160,000$

Differences between cost and fair values are not due to credit losses. The decline in fair value was properly accounted for at December $31,$ Year $3.$ Ball$$s Year $4$ statement of changes in equity should report an increase of

A$.$ $$30,000$

B$.$ $$20,000$

C$.$ $$10,000$

D$.$ $$0$