Please help me

Find a • b. a = 5i + 7j, b = -4i + 3j

A: <1, 10>

B: <-20, 21>

C: 1

D: 41

[tex]\bf \begin{cases} a=5i+7j\implies &\ \textless \ 5,7\ \textgreater \ \\ b=-4i+3j\implies &\ \textless \ -4,3\ \textgreater \ \end{cases} \\\\\\ \ \textless \ 5,7\ \textgreater \ \cdot \ \textless \ -4,3\ \textgreater \ \implies (5\cdot -4)+(7\cdot 3)\implies -20+21\implies 1[/tex]