Answer:
110,000 base 2
Step-by-step explanation:
column 1 [the first position in the number]:
1+1=0, (carry 1<u>)</u>
column 2:
0+1 +<u>1</u> <em>(carried)</em>=0, (carry 1)
column 3:
1+0+<u>1</u><em> (carried)</em>=0, (carry 1)
column 4:
0+1+1 <em>(carried)</em>=0, (carry 1)
column 5:
1+1+1=1, (carry 1)
then you write the last 1 'cause there is n number to add with:

In binary system the highest number to write is 1, if you add 1+1, it jumps to 0, and you have to carry 1 to the next position.
If you are not sure about the sum, you can convert the numbers in base 2, to base 10, so you can know if it is correct:

So 21+27=48.
<em>In decimal system when you add 9+1, it jumps to 0 and then you have to carry 1 to the next position, because the the highest number you can write is 9.</em>