The two triangles are similar triangles. The smaller triangle has hypotenuse 6 and a horizontal leg of 4 The large triangle has hypotenuse 6+12=18 and a horizontal leg of x, where x is some number larger than 4
Because the triangles are similar, we can form the proportion below and solve for x x/4 = 18/6 6*x = 4*18 6*x = 72 6*x/6 = 72/6 x = 12
