D=1.5 h=0.2 D=4.5x10000 H=10 Vol. Of coins=(pi)r^2×h v= pi.x0.75x0.75x0.2 Vol of cylinder=(pi)R^2xH V=pix2.25x2.25x10x10000 No.of coins= Vol of cylinder/vol of coins = =4,50,000 Hence, 45,00,000 coins are to be melted to form the required cylinder
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So, here's what we have got.
The coins are cylindrical, so for the coins....
r₁=1.5/2=0.75 cm
thickness is height here, so h₁=0.2 cm

Then for the cylinder..
r₂=4.5/2=2.25m=225 cm 
h₂=10 cm

so, we have got everything in cms, then all that is remained to do is to compare both ones.
so, both are cylinders.

Here the 'n' is the no. of the coins.

so, we've got 
(225)² (10) = (n) (0.75)² (0.2)
506250=(n) (0.5625) (0.2)
n= 506250*100000/5625*2
so, n=4,500,000 

[note: I think there may be a mistake because I'm not sure if the 
diameter of the main cylinder is 4.5 meters, I'd like to tell you to check out if that value is 4.5 cms.]

Hope it helped. ^_^