Ive been working through some examples in this book; and so far so good however Im on a question which does not make sense the way Im working it out seems to me to be correct however the answer directs me elsewhere.

The question is on hear force.

Determine the force required to punch 20 x 15 mm rectangular holes in am ild steel plate 8mm thick..

Now Ive done a similar question but with a circle instead of the rectangle..

I dont see the problem here..

Formulas which it prompts me to use is for Area = 20 x 15 x t (8) t = thickness..

Which is 2400 respectively. With this answer I multiply for the USS (ultimate shear strength of the material which is given mild steel = 360N .

And I get a figure of 864,000 or 864 KN..

The answer in the back of this book is 202kN. Im Stumped What Am I doing wrong?

Apologies if this is a bit to simple or It comes off as stupid. Its racking my brain...