Answer
$3321J$
Work Step by Step
We know that
$1 Btu=252.0 cal$
$\implies 3.15 Btu=3.15\times 252.0 cal$
We also know that
$1 cal=4.184J$
$3.15 Btu=3.15\times 252.0 \times 4.184=3321J$
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