Machine has 64 bit architecture and two word long instruction
A "64 bit architecture" with 32 bit registers is a bit unusual. 

Taking the numbers at face value, a 2-word instruction is 128 bit long, you need 6 bit to encode the instruction, 2x7 bits to specify two registers, leaving 108 bits for an "immediate" operand. The maximum value in the "immediate" operand is $2^{107}-1$. 

That's answering the question that you asked. What your instructor actually asked, and what he intended to ask, and what he thinks he asked, and what answer he wants to hear, nobody can know that.