you know that 400+400=800. how can this help you find 2400+3400?
The answer is.... wait for it...
Looking at the first equation, we see we are adding 4+4 =8 and using "00" to finish the addition. In other words, we are just adding the first numbers and using the zeros as place holders. So, in the second problem, add the 24+34 and use the "00" as place holders. I think this is the type of thinking that they are looking for in this problem.