I'm just going to assume you did all this correctly since I don't have time to check your working.
For part c(ii) you seek the second point of intersection between the normal, which is the line
y+2=21(x−4), and the original curve which is defined parametrically.
If both equations were Cartesian, I am sure you would know how to proceed and find points of intersection. The whole 'sub y from one equation into the other and solve for x' type of thing.
But since one eqn is Parametric, and the other is Cartesian, you still aim to end up solving a single equation in one variable.
Your Cartesian line has x,y in there but these can both be expressed in terms of the parameter t.
Hence, if you sub in the curve's defining x,y coordinates in terms of t into the normal line equation, you end up with one equation in t to solve.
If you got the correct normal, then t=1 is obviously one solution corresponding to the point of intersection where you constructed the normal.
You seek *different* solution for t, and once you have it you can sub it back into the curve's eqn to obtain the x,y coordinates.