This expression is another way to write the fraction $\displaystyle\frac{{7}}{{2}}\usepackage{cmbright}\Huge\$ , but it is not written as a complex number. A complex number is any number in the form $\displaystyle{a}+{b}{i}\usepackage{cmbright}\Huge\$ where a and b are real numbers. The fraction $\displaystyle\frac{{7}}{{2}}{i}\usepackage{cmbright}\Huge\$ is the imaginary part of this complex number.