Fraction word problem

Question

Need help with this question. A scientist had 3/4 of a bottle of a solution. She used 1/6 of the solution in an experiment. How much of the bottle did she use?

It seems like I should subtract them, which gives me 7/12, but a friend tells me I need to multiply, which is 1/8. If it is multiplication, I don't understand why.

Answer 1

She used 1/6 of the solution in an experiment.

Now if you want to know how much of it is left then,

3/4 - 1/6 = 9/12 - 2/12 = 7/12