Answer:

x = 16

Explanation:

Given,

Thickness of the pipe = 0.7cm

inner radius of the pipe (r )= 3.5cm

External radius of the pipe (R ) = (3.5+ 0.7 )cmor,4.2cm

length=5dm or,50cm

We know,

Total surface area of pipe = 2π (r+ R ) ( h+ R - r)

or, Total surface area of pipe= 2×22/7(3.5+4.2)(50+4.2-3.5)

= 44/7 × 7.7 × 50.7

=2453.88cm^2

So the answer should be 2453.88cm^2

Hope it helps.