How much time is remaining? The Program

You are given two strings, A and B. A is the current position at which your timer is at, and B is the position at which your timer will stop. Both strings are in the format m:ss. You must write a program that determines the amount of time left which should also be formatted as m:ss or mm:ss.

Example

0:00 0:01 -&gt; 0:01
0:55 1:00 -&gt; 0:05
1:45 3:15 -&gt; 1:30
Excel, 6 Bytes

=B1-A1


Assuming A is in cell A1 and B is in cell B1