Sometimes also called Cross Number Puzzles, they consist in the simultaneous resolution of 6 cryptarithms
Show Solution 304, 152, 2 // 42, 6, 252 // 346, 158, 504
By clicking on the button "Another one" the program will select puzzles with alternatively max 3 and 4 digits in each number from an archive of 20,000 arithmogriphs.
The arithmogriphs have been generated by my free (Italian) program EnCalc.
Each puzzle has a unique solution, but I cannot judge about how difficult is to find it. Since they have been generated by a random process, you'll find both easy and difficult ones.
Hovering the mouse over "Show solution" the numbers composing the solution will be shown. In any case, you can solve this kind of puzzles using the solver in the cryptarithms page, entering one equation in each text field.