1) Turn them into improper fraction
2) Multiply denominator by denominator, numerator by numerator.
3) Turn it back to mixed fraction
DONE!!
Examples:
\(1\dfrac{6}{13}\times 4\dfrac{17}{57}\\ =\dfrac{19}{13}\times \dfrac{245}{57}\\ =\dfrac{1}{13}\times \dfrac{245}{3}\\ =\dfrac{245}{39}\\ =6\dfrac{11}{39}\)
Of course you can simplify them, like what I did in step 2.