Question 139948
Since the triangles are similar, this means that the length of the sides are dependent on one another. In fact, these sides form the ratio:



{{{10/8=5/y}}} 



{{{(10/8)*y=5}}} Multiply both sides by y



{{{10*y=5*8}}} Multiply both sides by 8



{{{10*y=40}}} Multiply



{{{y=40/10}}} Divide both sides by 10



{{{y=4}}} Simplify




So our answer is  {{{y=4}}}