#### Answer

56

#### Work Step by Step

A 2x2 determinant can be calculated as $ad-bc$, where a is the upper-left entry, b is the upper-right entry, c is the lower-left entry, and d is the lower-right entry.
Since the entry c is 0, the term bc will be 0.
Therefore, value of the determinant will be $ad=7\times8=56$