The copper content of an alloy is 60%. If 1 kg of copper is added into the alloy, the copper content of the alloy will increase to 70%.

a. Find the original weight of the alloy.

b. Find the percentage change in the weight of the alloy.

I am learning about percentage change and found this question in my textbook. I don't know how to solve this question. Could you please help me? Thank you.