if we notice those tickmarks in the triangle, that simply means that those sides are twins, namely HL = LJ = 5 and so on, that also means that the line cutting them from the opposite vertex is a median.
so we have three medians, meeting at a certain point, namely the centroid.
a particular feature of the centroid is that it cuts all medians in a 2:1 ratio, namely GP : PL are in a 2:1 ratio, therefore
21)
[tex]\bf \cfrac{GP}{PL}=\cfrac{2}{1}\implies \cfrac{8}{PL}=2\implies \cfrac{8}{2}=PL\implies 4=PL\\\\[-0.35em]~\dotfill\\\\GL=GP+PL\implies GL=8+4\implies \boxed{GL=12}[/tex]
22)
well, we already know from 21) :).
23)
recall, since the lines are medians, both sides on the opposite side are twins, HL = LJ = 5.
24)
if we take a look at the triangle GLJ, is a right-triangle, so we can use the pythagorean theorem on it,
[tex]\bf \textit{using the pythagorean theorem}\\\\c^2=a^2+b^2\implies c=\sqrt{a^2+b^2}\qquad\begin{cases}c=\stackrel{hypotenuse}{GJ}\\a=\stackrel{adjacent}{\stackrel{LJ}{5}}\\b=\stackrel{opposite}{\stackrel{GL}{12}}\\\end{cases}\\\\\\GJ=\sqrt{5^2+12^2}\implies GJ=\sqrt{25+144}\implies GJ=\sqrt{169}\implies \boxed{GJ=13}[/tex]
