can be worked with algebraic expression, but a quicker way would be to work with hypothetical (yet consistent) numbers.
A quick look would reveal that 2100 can be used as the original number of total artifacts (before the regime change). Hence, the number of artifacts displayed = 700 and that kept in store = 1400.
During the regime change, 300 to 420 artifcats went missing.
Therefore, the remaining number of artifactsis between
(2100 - 300 = 1800) and (2100 - 420 = 1680)
In order to display the same number of artifacts as before the regime change (700), the fraction that needs to be kept in storage = (1800 - 700 = 1100) to (1680 - 700 = 980).
=> the fraction of artifacts in storage = (1100/1800 = 11/18) to (980/1680 = 7/12), hence the correct answer is D