This is a problem in stoichiometry and in using dimensional analysis.
2H+ (aq) + 2NO3- (aq) + NO (g) 3NO2 (g) + H2O (l) ... balanced equation
From the balanced equation, we see that the stoichiometry is 1 mol NO produces 3 mols NO2. We will use this relationship to find grams of NO2 formed from 1.49 grams of NO.
First, convert to moles:
moles NO used = 1.49 g NO x 1 mol NO/30.0 g = 0.0497 moles NO
Find moles NO2 produced:
0.0497 mols NO x 3 mols NO2/mol NO = 0.149 moles NO2 produced
Finally convert to grams:
0.149 moles NO2 x 46 g/mol = 6.85 g NO2 produced