Step-by-step explanation:
[tex](5 \sqrt{3} + \sqrt{15} ) \times (3 \sqrt{15} - \sqrt{15} ) \\ \\ = (5 \sqrt{3} + \sqrt{15} ) \times 2 \sqrt{15}\\ \\ = 5 \sqrt{3} \times 2 \sqrt{15} + \sqrt{15} \times 2 \sqrt{15} \\ \\ = 10 \sqrt{3 \times 15} + 2 \sqrt{ {15}^{2} } \\ \\ = 10 \sqrt{45} + 2 \times 15 \\ \\ = 10 \sqrt{9 \times 5} + 2 \times 15 \\ \\ = 10 \times 3\sqrt{ 5} + 30 \\ \\ = 30 \sqrt{5} + 30 \\ \\ = 30( \sqrt{5} + 1)[/tex]
