Can you prove this by structure induction?

I tried with every induction but I could not get it.

Please, show me all the steps, Thank you.

4. Simple expressions use the arithmetic operators + and *, with both numbers and variables allowed as operands. The recursive definition of such expressions is as follows: 1) Any number or letter (i.e., a variable) is an expression. 2) If E and F are expressions, then so are E+F, E* F, and (E). For example, both 2 and x are expressions by the basis. The inductive step tells us : +2, (+2), and 2 (0+2) are all expressions. Notice how each of these expressions depends on the previous ones being expressions. Prove that every expression has an equal number of left and right parentheses