Question 29929
Let the 20 tones bin be x
Let the 15 tones bin be y
x+y=30
y=30-x (susbitution)


20x+15y=510
Subsitute:
20x+15(30-x)=510
20x-15x=510-450
5x=60
x=12


y=30-12
y=18


<font color = brown>Hence, there are 12 (20 tones) bin and 18 (15 tones) bin.</font>
Paul.