Solve {l}{5=I*6800+G-9}{I=5/500*D/-6(6/-6+D/-12+1)}{15=I(3300+6800)+D-9}

$$\left. \begin{array} { l } { 5 = I \cdot 6800 + G - 9 } \\ { I = \frac { 5 } { 500 } \cdot \frac { D } { - 6 } ( \frac { 6 } { - 6 } + \frac { D } { - 12 } + 1 ) } \\ { 15 = I ( 3300 + 6800 ) + D - 9 } \end{array} \right.$$

Solve for I, G, D

$$I=\frac{3\sqrt{1221}}{255025}+\frac{123}{51005}\approx 0.00282258\text{, }G=\frac{-816\sqrt{1221}-24466}{10201}\approx -5.193543114\text{, }D=\frac{-12\sqrt{1221}-36}{101}\approx -4.508056683$$

$$I=-\frac{3\sqrt{1221}}{255025}+\frac{123}{51005}\approx 0.002000477\text{, }G=\frac{816\sqrt{1221}-24466}{10201}\approx 0.396758485\text{, }D=\frac{12\sqrt{1221}-36}{101}\approx 3.795185396$$