Let x = download size of the standard version.
4515 - x = download size of high quality version.
High quality was downloaded 4 times more so 4 x 4.8 = 19.2 = downloads of high quality versions.
Set up a ratio:
2.3 / 19.2 = x / 4515-x
Cross multiply:
2.3(4515-x) = 19.2x
10384.50 -2.3x = 19.2x
Add 2.3x to both sides:
10384.50 = 21.5x
Divide both sides by 21.5:
X = 10384.50/21.5
X = 483
There were 483 downloads of the standard version.