Kirchoff's Rules Homework: Solving 3 Unknowns in a Circuit

[fsm]

Homework Statement

This is the circuit I'm working on:

Homework Equations

My equations are:
4.64v=-200I1-800I3
4.64v=750I3+800I2
4.64v=-200I1-750I3

The Attempt at a Solution

I should have a third unknown in each equation. I not seeing where I'm going wrong. I'm supposed to put this in a 3X3 matrix and have Excel solve for the simultaneous equations. Any help?

 

[Dick]

There are three different loops that you can sum the voltages around in the problem. The one involving R2 and R3 does not include the battery. So the sum around that loop should be zero. Your first equation also has an 800I3. Typo?