Divide by 300 at the same time, and you get:

5x+7(50-x)=300

5x+350-7x=300

2x=50

x=25

(2)50x+20( 15—x)=440

Divided by 10 at the same time, we get:

5x+2( 15-x)=44

5x+30-2x=44

3x= 14

x= 14/3

(3) 1800x+600(40—x)=60000

Divide by 600 at the same time, and you get:

3x+(40-x)= 100

3x+40-x= 100

2x=60

x=30

(4)260×5x+ 150×6(20—x)= 24000

Divided by 10 at the same time, we get:

26×5x+ 15×6(20-x)=2400

Divide by 2 and divide by 5 at the same time to get:

13x+9(20-x)=240

13x+ 180-9x=240

4x=60

x= 15