[tex]\large\boxed{\begin{array}{l}\underline{\sf 2^a\,lei\,de\,Newton}\\\rm F_R=m\cdot a\\\underline{\sf c\acute alculo\,da\,forc_{\!\!,}a\,resultante}\\\rm F_R=60-20=40\,N\\\rm F_R=m\cdot a\longrightarrow m=\dfrac{F_R}{a}\\\\\rm m=\dfrac{40}{2}\\\\\rm m=20\,kg\\\huge\boxed{\boxed{\boxed{\boxed{\rm\dagger\red{\maltese}~\blue{alternativa~e}}}}}\end{array}}[/tex]
