[tex] \frac{21+39+48+a+b}{5}=84 \\ 108+a+b=420 \\a+b=312 \\ \\ \frac{64+2a}{2}=42 \\ 64+2a=84 \\2a=20 \\a=10 \\ \left \{ {{a=10} \atop {a+b=312}} \right. \\ \\ \left \{ {{a=10} \atop {10+b=312}} \right. \\ \\ \left \{ {{a=10} \atop {b=302}} \right.[/tex]
