數學 一元一次方程

1) 5mn - 3 = 4m 2n
5mn -4m = 2n 3
m(5n -4) = 2n 3
m= (2n 3)/(5n -4)
if n =2
m= (4 3)/(10-4)
m=7/6

2) ab=5(b-c)
ab= 5b -5c
ab -5b = -5c
b(a-5) = -5c
b= -5c/(a-5)
if a=1 c=2
b = -10/-4
b= 5/2

3) 3/8 x a =6
3a = 48
a = 16

5mn-3=4m+2n
5mn-4m=2n+3
m(5n-4)=2n+3
m=2n+3/5n-4
(點點點)m=2(2)+3/5(2)-4
m=7/6

ab=5(b-c)
ab=5b-5c
ab-5b=-5c
b(a-5)=-5c
b=-5c/a-5
b=5c/5-a

b=5(2)/5-(1)
b=10/4

第三題睇唔明 補比我thank you