ANSWER
[tex]5 {x}^{2} y[/tex]
EXPLANATION
The first expression is
[tex]15 {x}^{2} {y}^{3} [/tex]
This can be rewritten as
[tex]3 \times 5 \times {x}^{2} \times x \times {y}^{2} \times y[/tex]
The second expression is
[tex] - 20 {x}^{3} yz[/tex]
This can also be rewritten as,
[tex] = - {2}^{2} \times 5 \times {x}^{2} \times x \times y \times z[/tex]
The greatest common factors are;
[tex]5 \times {x}^{2} \times y = 5 {x}^{2} y[/tex]
