Calculate according to standard atomic weight, potassium nitrate (KNO3)'s nitrogen content is 14/(39+14+16*3) = 13.86%. So 101.1 g of potassium nitrate contains 101.1*13.86% = 14.01 g nitrogen. Urea CO(NH2)2's nitrogen content is 14*2/(12+16+14*2+1*4) = 46.67%, so to have the same amount of nitrogen, the mass of urea needs to be 14.01/46.67% = 30.02 g.