To do the sum of two numbers in scientific notation we must put them in the same exponent, therefore, if we want to sum
We must put both coefficients in 2 or 3, we can choose, I'll put the 2.8 in exponent 2, therefore
Now we can preserve the exponent and sum the coefficient
Therefore we have
But see that the result is not in scientific notation, so let's adjust it:
Therefore, the result in scientific notation is
The coefficient (green) is 3.53 and the exponent (yellow) is 3