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
