a scientist removed a sample of 39.1 grams of a chemical from a container. The sample was 5 3/4 grams less than 3/10 of the total mass of the chemical in the container. What was the total mass in grams of the chemical in the container before the scientist removed the sample of 39.1 grams? Show your work or explain how you got it

The first thing we must do for this case is to define variables:
 x: the total mass of the chemical in the container
 y: a sample of a chemical from a container
 We have the following equation:
 y = (3/10) x - 5 3/4
 Then, for y = 39.1 we have:
 39.1 = (3/10) x - 5 3/4
 Clearing x:
 (3/10) x = 39.1 + 5 3/4
 (3/10) x = 44.85
 x = (10/3) * (44.85)
 x = 149.5 grams
 Answer:
 the total mass in grams of the chemical in the container before the scientist removed the sample of 39.1 grams was:
 x = 149.5 grams