Questions about Python exec

In Python, we made a calculation using exec and eval in the for statement

lists = ["a=1", "b=2", "c=a+b"]
returned_list = []
for x in lists:
    exec(x)
    returned_list.append(eval(x))
print(returned_list)

If I write it like this, SyntaxError: invalid syntax comes out. We can use similar code in Shell, but can't we use eval in the function?

How can I solve this problem? I want to run a grammatical string that specifies the variables in the list, and create a function that uses that string.