Explanation:

According to the question
Diameter of the solid cylinder=2 cm
The solid cylinder is recast into a hollow cylinder of length 16 cm, external diameter of 20cm and thickness of2.5 cm
Volume of the cylinder = ∏r²h
Radius of the cylinder =1 cm
So, volume of the solid cylinder=∏1²h
Let the length of the solid cylinder be l
Volume of the hollow cylinder = ∏h(R²−r²)
Thickness of the cylinder = (R-r)
0.25=10-r
Internal radius of the cylinder is 9.75cm
Volume of the hollow cylinder = ∏16(100−95.0625)
Hence, the volume of the solid cylinder is equal to the volume of the hollow cylinder
Equation I = equation ii
∏12h= π*16(100-95.06)
=h=79.04cm
Length of the solid cylinder is 79.04 cm.