You can put this solution on YOUR website!
Those two equations for b anc c are correct.
The last one is the value equation that gives the value of the entire collection.
You use the value of each stamp multiplied by the number of each stamp to give the total value.
If you substitute your two equations from above into this equation,
you will solve for a.
Then you can back substitute to find b and c.
Try it and if you get stuck, post another question.