How do you find an unknown addend?

What is the synonym for the equasion in math 'nothing'? What is 0.000000000000000000000001673 in scientific notation? I have a very small US coin. One side has a six sided star and date 1858. Other side has like Roman numeral III inside a fancy C--what is it? 1.9 cm equals how many mm? What is 43 rounded to nearest 100? What is the synonym for silly? Why are signed numbers used? What does categorical data vary mean? Why is 4d time? What is the nearest tens of 46? What is the standard notation for 4.36 x 10 to the sixth power? How many hours in 1230 minutes? Do you have sets of multiple choice questions for arnis? What is homophone for add? 1.What is the name of a shape with two semi-circles connected by two straight lines that are tangential with the semi-circles 2.Is there a different name if the semi-circles are of different diameter? What is the answer for 5x plus 7 equals -4x plus 25? What is the number of real solutions in 4xsquared plus 16x plus 16 equal 0 D equal bsquared minus 4ac? Can there be such thing as unequal thirds? How many adavus in bharatanatyam? Are the lines that contain the altitudes of a triangle are parallel?