Find an equation for the horizontal tangent to the curve y=x-3root x

Hi

a ) find an equation for the horizontal tangent to the curve y=x-3root x

b) What is range of values of values of curve's slope ?

c ) What is range of values of curve ?

number a already I solved but my queation now in b and c

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I try to solve

b)

to get curve's slope must derivatives

range of values of values of curve's slope is ( - infinity , 1 ]

becuse when we put ( 0 ) in curve's slope It will comw 1

c ) did here put zero in y=x-3root x

please help me .