These puzzles be good starters, note the Algebraic version.
For a new kind of puzzle Yohakuu is a puzzle that will test your number sense and problem solving skills. Each Yohaku puzzle is either an additive or a multiplicative puzzle. You must fill in the empty cells such that they give the sum or product shown in each row and column as well as satisfying a rule if given.
Choose from 2×2, 3×3 or 4×4 puzzles.
Follow Yohaku on Twitter. Checking the Twitter stream I noted this algebraic puzzle below, an excellent idea. Try a little logic, where must c be placed for example.