Answer:
240 standard versions of the song were downloaded
(and 630 high-quality versions of the song were downloaded)
Explanation:
Let the downloads of the standard version be x
And the downloads of the high-quality version be y
Since the total downloads were 870, so we get,
x + y = 870 (i)
Also, The total download size was 3381 MB
Meaning the size of the high-quality downloads + the size of the standard version downloads = 3381
so,
Solving these to get x and y,

Using (i), we get,
x = 870 - y
putting this value of x into (ii), we get,

Putting this into the equation,
x = 870 - y, we get,
x = 870 - 630
x = 240
Hence, 240 standard versions of the song were downloaded and 630 high-quality versions of the song were downloaded