How to. automate nutrition calculation

Given a vector of quantities:

fbs = {6.18*10^6, 2.663*10^6, 1.4735*10^7};

I like to create the following code:

kcal = WolframAlpha["6.18`*^6 tons of wheat + 2.663`*^6 tons of potato +       1.4735`*^7 tons of vegetables", {{"CaloriesPlus", 1}, "ComputableData"}];

by replacing the quantities in fbs in kcal. The question is how to insert the numbers in fbs into the numbers in kcal, which are strings.

Thanks