Find the Cardinal Number of the Indicated Set $\mathrm { n } ( \mathrm { A } ) = 7 , \mathrm { n } ( \mathrm { B } ) = 15$

Multiple Choice

Find the cardinal number of the indicated set. Use the cardinal number formula.
-If $\mathrm { n } ( \mathrm { A } ) = 7 , \mathrm { n } ( \mathrm { B } ) = 15$ and $\mathrm { n } ( \mathrm { A } \cap \mathrm { B } ) = 5$ , what is $\mathrm { n } ( \mathrm { A } \cup \mathrm { B } )$ ?

A) 16
B) 18
C) 22
D) 17