multiply this radical expression

simplify | (19 sqrt(h) + 4 sqrt(2 h)) (19 sqrt(h) - 4 sqrt(2 h))
361h - 76sqrt(2)h + 76sqrt(2)h - 32h
361h - 32h 
329h

Note that     (a + b)(a - b)  =  a² - b²

So...           $({\color{violet}\,19\sqrt{h}} + {\color{blue}4\sqrt{2h}})({\color{violet}\,19\sqrt{h}} - {\color{blue}4\sqrt{2h}})\,=\,({\color{violet}\,19\sqrt{h}})^2-( {\color{blue}4\sqrt{2h}})^2$

$(\,19\sqrt{h})^2-( 4\sqrt{2h})^2 \\~\\ =\,19*19*\sqrt{h}*\sqrt{h}-4*4*\sqrt{2h}*\sqrt{2h} \\~\\ =\,361h-16*2h \\~\\ =\,361h-32h \\~\\ =\,329h$