Question

Please help, thanks.

Answer 1

Use the pythagoras theorem
12^2 = 3^2 + h^2
h =  3√15 
h = 11.618950038622 (exact)
h = 11.62 (approximate)

Answer 2

$\text{Apply Pythagorean theorem,}\\ \\~~~~~~12^2 = 3^2 + h^2\\\\\implies h^2 = 12^2 -3^2\\\\\implies h^2 = 144-9\\\\\implies h^2 = 135\\\\\implies h = \sqrt{135}\\\\\implies h = 3\sqrt{15}\\\\\implies h \approx 11.62$