sell of truck and trailer-tax form 4797

does anyone know how to fill out form 4797--we retired last year-we sold our truck and trailer for 25,000==I know that you fill out section III lines 19 thru 24-truck and trailer is fully depreciated--so total gain is 25,000 then you put 25,000 on line 30 is this correct??? where else on the form does it go? I hope someone can help I just cant go to spending money for someone to fill out this form. this is my last business taxes-I just cant make sense out of the irs instructions