2)

Given: $$a/2 = 2.4$$, $$h = 6.8$$ cm.
The calculation for $$h$$ seems to be $$h = \sqrt{70^2 - 2.5^2}$$ or similar, resulting in $$h=6.8$$ cm.
The final part of the calculation involves $$a/2 = 2.9$$ cm and $$h_s$$.