find the perimeter with a diameter 22 mm and a semi circle

The formula for the circumference is πd (pi times diameter).  First you apply that then since it is a semi-circle you divide it by 2 and there you get your answer!.

So it would be:

π(22) then you divide it by two.

Also I forgot the formula for circumference isn't really that its 2πr (two times pi times radius), but if you simplify that its essentialy πd

I think that you both forgot to add the 22mm for the straight side!