By using the formula here are the answers:
Top row: A - 117mm B - 103mm C - 233mm
Bottom row: A - 202mm B - 57mm C - 232mm
here is the work
Top row A: 10^2 + 6^2 = x^2 136 =x^2, or sqrt136 cm = 11.66 cm=116.6 mm=117 mm by rounding
Top row B: 9^2+5^2 = x^2 106=x^2 or sqrt106=x = 10.3cm = 103mm
Top row C: 20^2+12^2=x^2 = 544=x^2=sqrt544 = x = 23.3cm=x = 233mm
Bottom row A: 23^2=11^2+x^2 = 529=121+x^2 = x^2=408 = sqrt408=x = 20.2cm = 202mm
Bottom row B: 9^2=7^2+x^2 = 81 = 49+x^2 = x^2=32 = sqrt32=x = 5.7cm = 57mm
Bottom row C: 30^2=19^2+x^2 = 900=361+x^2 = 539=x^2 = sqrt539 = x = 23.2 cm or 232mm
Hope this helps :)