Use the rule:
[tex]\left| \left[\begin{array}{ccc}a&b&c\\d&e&f\\g&h&i\end{array}\right] \right|=[/tex]
[tex]=a\cdot e\cdot i+d\cdot h\cdot c+b\cdot f\cdot g-c\cdot e\cdot g-f\cdot h\cdot a- b\cdot d\cdot i [/tex].
Then,
[tex]\left| \left[\begin{array}{ccc}-2&2&b\\0&3&a\\0&0&-5\end{array}\right] \right|=[/tex]
[tex]=-2\cdot 3\cdot (-5)+2\cdot a\cdot 0+0\cdot 0\cdot b-b\cdot 3\cdot 0-a\cdot 0\cdot (-2)- 0\cdot 2\cdot (-5)=30 [/tex].
Answer: 30
