How many metamers are possible for C4H10O?

The metamers are those isomers which differ with respect to the nature of alkyl group around the same divalent functional group.

That means if there is a functional group, we must not change it, but we can change the alkyl groups connected with the functional group. 

thus based on the structure C4H10O We can get three ethers as metamars. And they are:

1. Ethoxyethane
2. 1-methoxypropane
3. 2-methoxypropane