Start by taking your tank top and folding it down below the underarms. Trace the pattern on to your print dress making sure to measure your hips and mark that correctly as well. Cut your piece out and you should have something like this:
Turn your right sides together, pin and sew along side seams.
Take your tank top and draw a straight line across at underarms. Cut making sure to leave a little room for seam allowance.
Turn your cut tank piece inside out and pin it to the top of your dress-- and sew.