You correctly substituted the value 300,000 into the equation and divided both sides by 100,000 to get $\displaystyle{3}={{10}}^{{{0.02}{t}}}\usepackage{cmbright}\Huge\$ . However, you incorrectly divided both sides by $\displaystyle{0.02}\cdot{10}\usepackage{cmbright}\Huge\$ while trying to isolate the variable. You should instead take logarithms of both sides.