A( 1- 1/4)= 1/4 A+B-30

A = 100

B =80

2、x/( 1-4/9)= x/( 1-9/ 19)-2，x=20

20/( 1-4/9)=36

3、3(s-20)+ 15=2s

s=45

4.12.56/2 * 6 *100 = 3768 (cubic centimeter)

5、( 12/2)? *3. 14*8* 1/3=(4/2)? *3. 14*x

x=24