Mean of 1st 4 terms is 77.

Assume that the terms are in arithmetic series .

Mean(m).

Multiply 4 to each side.

Group like terms.

When 5th and 6th terms are included, mean(m) increased by 32, then

                         (from equation (1))

Multiply 6 to each side.

Subtract 308 from each side.

Multiply 2 to equation (2).

From equations (1) and (3).

Subtract (1) from (3).

Substitute in equation (1).

So the 1st term is 29.