In Exercises $5-6, a$ stone is tossed vertically into the air from ground level with an initial velocity of 15 $\mathrm{m} / \mathrm{s} .$ Its height at time $t$ is $h(t)=$ $15 t-4.9 t^{2} \mathrm{m}$ Compute the stone's average velocity over the time intervals $[1,1.01],[1,1.001],[1,1.0001]$ and $[0.99,1],[0.999,1],[0.9999,1]$ and then estimate the instantaneous velocity at $t=1$