The notation in its current form isn't entirely clear.
Did you mean to write [tex]\frac{3\sqrt{10}}{4}[/tex]? The 4 isn't in the square root.
If so, then the expression is in simplest form because we cannot simplify [tex]\sqrt{10}[/tex] any further (note how 10 doesn't have any perfect square factors other than 1).
Also, the 3/4 portion is fully reduced already.
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Or,
Did you mean to write [tex]3\sqrt{\frac{10}{4}}[/tex] ? This time the 4 is inside the square root.
If so, then we can simplify like this
[tex]3\sqrt{\frac{10}{4}}\\\\\frac{3\sqrt{10}}{\sqrt{4}}\\\\\frac{3\sqrt{10}}{2}\\\\[/tex]
This means that [tex]3\sqrt{\frac{10}{4}}=\frac{3\sqrt{10}}{2}\\\\[/tex]
