Answer:
The amount of thistle bird seed she purchased was 7.5 pounds
Step-by-step explanation:
Let
x ----> the amount in pounds of thistle bird seed she purchased
x ----> the amount in pounds of wild bird seed she purchased
we know that
Kate bought $23.40 worth of two types of bird seed.
so
----> equation A
She bought 12 pounds of wild bird seed
so

substitute the value of y in the equation A

solve for x

therefore
The amount of thistle bird seed she purchased was 7.5 pounds