When you add in scientific notation, all powers if ten have to be the same. In the first equation, just change the 1.4•10^4 into 14•10^3, then add the coefficients
6.4+14+7.5=27.9•10^3
Your answer should be chaged to 2.79•10^4 to keep it in correct scientific notation.
The second problem is dont the exact same way, just subtract
