take the silver production number (and assume produced = sold 1:1)
work out the average London fix spot price for silver in the period (U$31.66/oz)
take the cash cost number and subtract it from the avg price (negative U$4.52, so in effect you're adding)
multiply the production with the revenue per ounce.
To work out the Mine Operating Income (MOI) in a ballpark way for the 1q11 quarter just announced in this NR, what you do is;
The answer is U$15.82m. Then you have other deductions, including smelter, G&A, tax etc. But you should get the picture from comparing that $15.82m number with previous quarters.