Answer
See the answer below.
Work Step by Step
$B.O.=N.\ Shared\ pairs\div N.\ links$
CO bonds:
$HCO_2^-$: $3/2=1.5$
$CH_3OH$: $1/1=1$
$CO_3^{2-}$: $4/3=1.33$
Since bond length decreases with bond order, the CO bonds will be the longest in $CH_3OH$ and the shortest in $HCO_2^-$.
