Respuesta :

Answer:

4.2mm

Step-by-step explanation:

This are two similar triangles.

Comparing the two:

8/3 = (7+x)/x

Cross multiplying

8x = 3 (7+x)

8x = 21 + 3x

8x - 3x = 21

5x = 21

Dividing by 5

X = 21/5

X = 4.2mm