copy value from another worksheet using formula

Hi All,

I have two worksheets namely LTA & INV. I have a few columns in LTA and INV.
I want to copy the values from a column in INV to LTA after I compare two
columns in LTA & INV if matches copy the column from INV to LTA. For Example

INV.XLS
INV NO LIC NO
100 100
101 101
102 102
103 103
104 104
105 105

LTA.XLS
BILL NO VEH NO
100
101
102
103
104
105

See in the above example my column BILL NO in LTA is blank now I want to
copy this column from INV.XLS column INV NO after LIC NO and VEH NO matches.

Can anyone help me in this regard? Thanks in advance