You can use F.O.I.L. for this, which if you don't know stands for first outer inner last, so multiply the first in each parentheses, then the outer, then the inner, then the last. yours would be 3*5+3*√7+(-√7)*5+(-√7)*√7 => 15+3√7-5√7-7 => 8-2√7 Final answer: 8-2√7 Hope I could help :)
