Think about the place values of each of the digits and add like parts. In the first number, the 1 means 1 whole and the 3 means 3 wholes, so adding them, we get 4 wholes.
Now we can add the total number of hundreds. In the first number, there are 2 tenths, or 20 hundreds. In the second number, there are only 4 hundredths. So combined we have 20 + 4 = 24 hundreds.
4 wholes and 24 hundredths is written 4.24.
Follow the same steps as in part (a).