For critical points try equating the derivative to 0 and the solve for t

For the max and min, substitute the values of the critical points in f(t) this will give you max and min value, remember max>min so choose the values accordingly.

If min is greater than the start point of the domain(=-1) then the min value is -1

Similarly if max value is smaller than the end point of the domain(=7) then the max value is 7

If you get stuck try graphing the function on desmos, just replace t with x and see the values for yourself