What is the conjugate of the given complex number?

z = 3i + 7

Correct option is B

​$$\begin{aligned}&\text{The conjugate of a complex number } z = a + bi \text{ is denoted as } \overline{z} \text{ and is defined as:} \\&\overline{z} = a - bi \\[10pt]&\text{Here, the \textbf{real part} } (a) \text{ remains the same, while the \textbf{imaginary part} } (b) \text{ changes sign.} \\[15pt]&\text{Given:} \\&\qquad z = 7 + 3i \\[5pt]&\bullet\ \text{Real part } (a) = 7 \\&\bullet\ \text{Imaginary part } (b) = 3 \\[5pt]&\text{The conjugate is:} \\&\qquad \overline{z} = 7 - 3i\end{aligned}$$​​