Hello, I have formulated the following problem similar to a problem in a book I read, but not the same. Using an online circuit editor I have managed to find node voltage calculations to check my work; unfortunately I don't have any idea as to how to incorporate current sources in mesh analysis.
I have named the leftmost mesh current as I_a, the upper middle as I_b, the lower middle as I_c, and the rightmost as I_d. (And have assumed a clockwise direction for all of them)
I have formulated the following mesh equation for I_c:

5(I_c-I_a)+6(I_c-I_c)+7(I_c-I_d)=0
I have no idea how to formulate the mesh equations for I_a, I_b, and I_d - if you could I would greatly appreciate an example of how to formulate any of the mesh equations for those currents.

I've done a similar problem before with the current source being part of two meshes (and Wikipedia instructed me to create a supermesh and relate the equations), but I'm not sure how that would apply here.

 

You've got a typo in your one equation; it should be:

5(I_c-I_a)+6(I_c-I_b)+7(I_c-I_d)=0

The other 3 equations you need are simply:

I_a = 4
I_b = 3
I_d = -2

 

You've got a typo in your one equation; it should be:

5(I_c-I_a)+6(I_c-I_b)+7(I_c-I_d)=0

The other 3 equations you need are simply:

I_a = 4
I_b = 3
I_d = -2

I see - so the constant current simply determines the current of that series. (I had suspected so, but I was having second doubts.)

Thanks!