阅读理解

    Read the following advertisement and answer the questions below according to the table.

    SECRETARY TV

    Major network looking for secretary/gal/guy. Friday to work on various temporary assignments. Work 1，2，3，4 or 5 days a week. Mr. Newcomb 889-0030

    SECRETARY QUEENS

    Good skills, General insurance agency. Richmond Hill area.

    849-8760

    SECRETARY. P/T.

    Steno, type, hrs, Mon.-Fri., 10-1 and/or Mon. Wed. & Fri. 2:30-7:00.

    Tues.2:30-5:00 Midtown office 355-5743 after 7 p.m.

    SECRETARY

    Small midtown law firm. Excel skills, no legal exp req'd. 755-2040

    SECRETARY.

    Fast-moving ad agency needs bright, energetic, good typist for various responsibilities. 684-2500

    （P/T.=part time; Steno=stenographer速记员；exp=experienced；req'd=required）

一个物体的运动方程为$s=t^2$其中$s$的单位是米,$t$的单位是秒,那么物体，在$3$秒末的瞬时速度是    米/秒

如图，等边△OAB的边OB在轴的负半轴上，双曲线$y=\frac{k}{x}$过OA的中点C，已知等边三角形的边长是4，则该双曲线的表达式为(    )