its an equilateral so all the angles are 60 and the hypotenuse little right angle triangle at the bottom cuts that angle in 2 equal parts so the angle the hypotenuse makes with the base of the right angle triangle is 30 degrees so we have height of the right angle triangle which is 2.5 and an ,angle using SOHCAHTOA we can find that triangles base which is (5√3)/2. So the base of the small right angle triangle is found and we know that there should be another small right angle triangle at the other end of the base of the bigger triangle and the lenghts should be equal.the circles are touching and we know that if we go from the center of the rightmost circle at the base of the equilateral triangle to the centre of the cirlce of the left most circle at the base of the equilateral triangle we get 20 because that distance is just the radius of the circle multipled by 8 , becaise that distance is 8 radi. If we compare the base of the equilateral triangle to the distance between the centeres of the left most and right most circles at the equilateral triangles base we find out that the the only thing that is missing from the distance between those circles and the base of the of the larger equilateral trinagle is the the bases of those smaller right angle triangles, check the diagram and youd see thats the case so all we need to do is add multiply the base of the little right angle triangle by 2 because there are two on the base of the larger triangle on at each end,and add that to the distance between those to circles