Question: So here's the question:

***We want to design a circuit that determines if a four-bit number is less than 10 and is also even.***

***a. (10 points) Write an expression of M such that M=1 if the four-bit number X (x3 x2 x1 x0) is less than 10
and is also even.***

Is this asking for the answer in POS form since it is using "M" instead of "m"?

Answer: 
They probably want the simplest form.
Yes. The conventional representation for the POS form is M(.). Now, since the last bit for the even numbers is 0, it is enough to have 3 bits will all numbers from 0 to 4. So, we just need a mod 5 counter to generate all these numbers and the last bit of the four bits (LSB) being grounded always.