To subtract numbers in scientific notation, we have to bring both to same powers of 10.
Let's change the first number to 10 to the power 8.
So, it will become:

So, we have to perform:

Now we simply perform the subtraction and tag along 10 to the power 8.
So,
1.3 - 0.00253 = 1.29747
So, answer is:
