Answer :
[tex]x - \hbox{one number}\\
x+3 - \hbox{ the other number}\\\\
x+x+3=43\\
2x=40\\
\boxed{x=20}\\
\boxed{x+3=23}[/tex]
[tex]x-first\ number\\x+3-second\ number\\x+(x+3)=x+x+3=2x+3-the\ sum\ of\ these\ numbers\\43-the\ sum\ of\ these\ numbers\\\\therefore\\\\2x+3=43\ \ \ \ |subtract\ 3\ from\ both\ sides\\2x=40\ \ \ \ \ |divide\ both\ sides\ by\ 2\\x=20-first\ number\\x+3=20+3=23-second\ number\\\\Answer:\boxed{20\ and\ 23}[/tex]