Factorize the following:
(a) $15 x^{2} y^{2}+20 x y^{3}$
(b) $14 a^{3} b-12 a^{2} b^{2}$
(c) $2 x^{2}+3 x y-10 x-15 y$
(d) $4 x y-7 y^{2}-12 x+21 y$
(e) $15 x^{2}+8 y+20 x y+6 x$
(f) $6 x y-20+15 x-8 y$
(g) $9 x^{2}+24 x y+16 y^{2}$
(h) $16 x^{2}-40 x y+25 y^{2}$
(i) $25 x^{3} y^{4}-16 x y^{2}$
(j) $(2 x+5 y)^{2}-(x-3 y)^{2}$