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)
![\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}](https://img.qammunity.org/2019/formulas/mathematics/college/2nhnkqx1v320x6ugql44917n3ahkxbmoij.png)
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,
