6. i. A student was asked to solve the equation \(2 ^ { 2 x + 4 } - 9 \left( 2 ^ { x } \right) = 0\). The student's attempt is written out below. $$\begin{gathered} 2 ^ { 2 x + 4 } - 9 \left( 2 ^ { x } \right) = 0
2 ^ { 2 x } + 2 ^ { 4 } - 9 \left( 2 ^ { x } \right) = 0
\text { Let } y = 2 ^ { x }
y ^ { 2 } - 9 y + 8 = 0
( y - 8 ) ( y - 1 ) = 0
y = 8 \text { or } y = 1
\text { So } x = 3 \text { or } x = 0 \end{gathered}$$ Identify the two mistakes that the student has made.
ii. Solve the equation \(2 ^ { 2 x + 4 } - 9 \left( 2 ^ { x } \right) = 0\), giving your answer in exact form.