So we have the numbers of one triangle and one number from another triangle (congruent triangles have congruent corresponding sides) do cross multiplication Altitude over altitude = side over side
SH/FJ = ST/FG to substitute 5/7 = 6/x cross multiplication (5) (x) = (7)(6) 5x = 42 divide both sides by 5 to isolate the x x = 8.4