Suppose x is a positive integer with n digits, say x = dd2d3 dn. In other words, di {0, 1, 2, ..., 9} for 1 i n, but d #0. Here's a definition: For a, b Z, a is a divisor of b if b = ak, for some k Z. Please prove the following statement: If 9 is a divisor of d + d + + dn, then 9 is a divisor of x.