Capital gains on modular home sale

I'm currently under contract on a property that has two residences on it. One is a house that I plan on living in, and the other is a modular home. I'm financing the property temporarily as a commercial investment property to allow for the sale of the modular home, and later convert to a conventional 30 year fixed rate mortgage. My question is how will the sale of the mobile home be taxed in regards to capital gains? From my understanding the gains would be taxed at my normal tax rate due to being short term, but how would the taxable amount be determined?