Structural Mechanics

In a potential flow, a uniform stream of strength U directed along the x-axis and four line sources (2-dimensional) of strengths , , ,2 3 4 5    -- are placed along the x-axis at x = 0, 1, 2 and 3, respectively. The strength of an additional line source to be placed at 4x = such that a closed streamline encircles all five sources is _____. (round off to two decimal places).