Every class boundary of a distribution is increased by 8, so 0-10 becomes 8-18, 10-20 becomes 18-28, and so on. The frequencies stay the same. The median:

In Median = $l+\left(\frac{n/2-cf}{f}\right)\times h$ only $l$ is affected: every lower boundary rises by 8 while $n,cf,f$ and the class size $h=10$ are untouched. So the median rises by exactly 8. It would be multiplied by 8 only if every boundary were multiplied by 8; 4 is half the shift, which no term in the formula produces; and it is unchanged only if the boundaries are unchanged — that is what happens when the FREQUENCIES are scaled instead.