let's say, the number is "a".
what's three times "a"? well, 3*a or 3a.
ok... what's four more than that? well, 3a + 4
what's the square root of that? well, [tex]\bf \sqrt{3a+4}[/tex]
alrite, and we know that's equal to 7...so
[tex]\bf \sqrt{3a+4}=7\impliedby \textit{squaring both sides}
\\\\\\
(\sqrt{3a+4})^2=7^2\implies 3a+4=49\implies 3a=45\implies a=\cfrac{45}{3}
\\\\\\
\boxed{a=15}[/tex]
