1.a=5b ; b=c/3 => c=3b ; c=2d ; d=e/3 => e=3d ; e=99 => d=33, c=66, b=22, a=110.
2.a=b/9 => b=9a ; b=c/2 => c=2b ; c=d-96 ; d=2e ; e=21×4=84 => d=168, c=72, b=36, a=4.
3.e=18, d=9, c=60, b=20, a=35.
4.e=114, d=19, c=32, b=288, a=12.
5.e=23, d=27, c=9, b=1, a=10.
6.e=50, d=300, c=30, b=90, a=1.