algebra
posted by Babs .
Hi
I need a formula for the following word problem.
The cost of a cellphone has increased by 400% over 10 years. Does this correspond to a decrease of 4 times its cost?

What is the question?
if the current cost is $x
then the cost 10 years ago was $x/4 
A chemist is using
389
milliliters of a solution of acid and water. If
19.5%
of the solution is acid, how many milliliters of acid are there? Round your answer to the nearest tenth.