I agree with 4.a) as it definitely looks like the function's domain and range are defined for all the reals, so therefore must be its inverse. I also agree with 4.b), inverse functions are reflected about the line y = x. As for part c), you should know that multiplying the function by 3 will result is a dilation of the function (a vertical stretch of factor 3) and subtracting 1 will then move the function down one unit.

I agree with your answers to 5. Well done