A vinegar sample is found to have a density of 1.006 {\rm{ g/mL}} and to contain 4.2\% acetic acid by mass.How many grams of acetic acid are present in 1.20L of this vinegar?

Answer 1

1,200 L x 1.006 g/mL x 0.042 = mass acetic acid.
You make the problem hard to read by typing {\rm{g/mL}} and 4.2\%.
Density is measured in g/mL and w/w percent in %; those extra symbols are not necessary and completely useless (in my opinion) unless you have some specific reason for including them. If you do I would like to know what they are.