Convert the following decimal numbers to 6-bit two’s complement binary numbers and subtract them. Indicate whether or not the difference overflows a 6-bit result.
(a) 18₁₀ − 12₁₀ 
(b) 30₁₀ − 9₁₀ 
(c) −28₁₀ − 3₁₀ 
(d) −16₁₀ −21₁₀