In the complex plane, the two given points are represented by

and

. The midpoint would then be

which represents the complex number

.
To simplify these expressions, you can either use a calculator (which I'm assuming your teacher doesn't want you to do) or FOIL (distribute).
The first one would be:

The second one would be:
First, convert 1 1/4 into an improper fraction which is 5/4
Then, convert 5/4 making sure that the denominator is 8 in order to compare it with 5/8. (5/4 = 10/8)
Since you now know that 5/4 is equal to 10/8, now you can compare and see how much bigger 10/8 is than 5/8.
10/8 - 5/8 = 5/8
So, 1 1/4 is 5/8 greater than 5/8