I know this post is older, but I felt the need to comment . . .wasn’t this person trying to change the value of B to 26 by typing the syntax backwards . . 9 += b. .?
Even if that is what they were trying to do the = assignment operator works assigning what is to the right of it to the left of it. += is a shorthand to avoid writing num = num + 3 and just write num += 3
Backward syntax doesn’t exist, so, 9 += b means 9 = 9 + b, which is not something that can be done.