Answer:
140 quarts of olive oil
Explanation:
we know that
A restaurant uses 80% of its oil in one week.
They now have 28 quarts of olive oil left

so
28 quarts of olive oil correspond to the 20%
see the attached figure to better understand the problem
by proportion
Find out the the number of quarts the restaurant had at the beginning of the week (100%)
Let
x ----> the number of quarts the restaurant had at the beginning of the week

Complete the double number line attached