Question

I need some simple equations that equal 12,20,21,31.

Answer 1

(3 • 2) • 2 = 12, (3 • 7) - 1 = 20, (3 • 2) + (3 • 5) = 21, (6 • 5) +1 = 31

Answer 2

2*(3+6)=12      (2*2)*5=20            (3*4)*7=21     1+(5*6)=31