the 1-pin row into the 4-pin row requires all 3 moves. There are
no moves left to complete the solution of the problem.
the 3-pin row into the 4-pin row would require moving the 3 pins
above the 3-pin row, plus one of the pins at either end of the 4-pin
row. That is more than 3 moves.
Since neither the 1-pin nor the 3-pin row can become the 4-pin row,
it must be that the 2-pin row will become the 4-pin row.
the 2 pins from the ends of the 4-pin row to the end positions of the
2-pin row. Then move the top pin down to the front of the triangle.