The growth of the virus is considered exponential.
Thus the expression is,

Given,
A virus takes 16 days to grow from 100 to 190.
Thus,

Putting ln on both side we have
ln(190/100)=16k
0.64=16k
k=0.04
Similarly,

Solving,
ln(760/100)=0.04t
t=50.70
Thus required days is 51 (rounding off to whole number)