Design a combinational converter from a 4-bit BCD digit to its Excess-3 code. Excess-3 adds 3 to the BCD value, so 0000 (0) becomes 0011 and 1001 (9) becomes 1100. Input: bcd, a 4-bit BCD digit (only the legal values 0 to 9 are tested). Output: ex3, the 4-bit Excess-3 code. The testbench applies all ten legal digits and compares ex3 with the expected code.