x^2-7x+12=0
(x-3)(x-4)=0
x1=3 x2=4
bc=4,ac=3
ab=√(4^2-3^2)=√7
√7:7.5=3:a'c'
a'c'=22.5/√7≈8.5
√7:7.5=4:b'c'
b'c=30/√7≈11.34