Answer
x = 7.5
Explanation
This is a case of similar triangles.
Similar triangles have bigger triangles which have sides which are multiples of smaller triangles sides.
We know that the adjacent side of the bigger triangle is 6 and for the smaller triangle it’s 4 so the constant factor by which the sides of the small triangle are multiplied to obtain the sides of the large triangle is
6/4 = 3/2
Since we know the hypotenuse of the smaller triangle is 5.
Multiply this by 3/2 to get the hypotenuse of the bigger triangle
3/2 • 5 = 7.5
Hope this helped