Question Number 20203 by mondodotto@gmail.com last updated on 24/Aug/17
Commented by Einstein Newton last updated on 24/Aug/17
$$\left(\mathrm{a}\right)\:\mathrm{20}\:+\:\mathrm{37}\:−\:\mathrm{12}\:=\:\mathrm{45} \\ $$$$\left(\mathrm{b}\right)\:\mathrm{20}\:+\:\mathrm{37}\:=\:\mathrm{57} \\ $$