I assume byte addressable memory- nothing smaller than a byte can be used.
We have four digits. So, to represent signed 4 digit numbers we need 5 bytes- 4 for four digits and 1 for the sign (like -7354). So, required memory = 5 bytes
Now, if we use integer, the largest number needed to represent is 9999 and this requires 2 bytes of memory for signed representation (one byte can represent only 256 unique integers).
So, memory savings while using integer is $\frac{(5 - 2)}{5} = \frac{3}{5} = 60\%$
Correct Answer: $C$