(a-b)*10%=(a-2b)*12%
0.1a-0.1b=0.12a+0.24b
0.02a=0.14b
a=7b
(a-2b)*12%=(a-3b)*x
(7b-2b)*0.12=(7b-3b)*x
0.6b=4bx
x=0.6b÷4b
x=0.15=15%