We can think of roots as x. For example, 2 [tex] \sqrt{5} [/tex] can be 2x. Just treat it the same way. (but not the exact numbers!)
(2√5 + 3√7)²
(2√5 + 3√7)(2√5 + 3√7)
Distribute.
4√25+6√35+6√35+9√49
Simplify.
4(5)+12√35+9(7)
30+63+12√35
83+12√35 is your answer.