Question 374965
Use the FOIL method,
{{{(5*sqrt(6)-15*sqrt(3))*(4*sqrt(6)+12*sqrt(3))=20*6+60*sqrt(18)-60*sqrt(18)-180*3}}}
{{{(5*sqrt(6)-15*sqrt(3))*(4*sqrt(6)+12*sqrt(3))=120-540}}}
{{{highlight((5*sqrt(6)-15*sqrt(3))*(4*sqrt(6)+12*sqrt(3))=-420)}}}