Pre cal word problems

Question

To build a garden you need 10ft^{3 if soil containing 17% clay. You have 2 type of soul you can combine to achieve this. Soul with 35% clay and soul with 10% clay. How many ch of each soul should you use?} 

 

I need to formula 

Answer 1

c represents the amount of 35% clay

10 - c represents the amount of 10% clay

 

0.35c + 0.10(10 - c) = 0.17(10)

 

Can you solve for c and answer?