JS mathmatic problem [SOLVED]

Question

Is there value of ❝ a ❞ 7 ? Because the output is 9.
But how!! Pls explain.
https://code.sololearn.com/WGWlmEbG1FXl/?ref=app

Answer 1

a+=b is same as a = a+b(5+2), now a is 7
then, console.log(a+b),7+2 = 9

Answer 2

Lily Mea Thank you sooo much!!