Right, as you mentioned in the comments, you find [tex]d[/tex] by plugging in the different values of [tex]t[/tex].
For [tex]t=1\,\mathrm s[/tex], we have
[tex]d=\dfrac12\left(9.81\,\dfrac{\mathrm m}{\mathrm s^2}\right)(1\,\mathrm s)^2[/tex]
[tex]d=\left(4.905\,\dfrac{\mathrm m}{\mathrm s^2}\right)\left(1\,\mathrm s^2\right)[/tex]
[tex]d=4.905\,\mathrm m[/tex]
Similarly, for [tex]t=2\,\mathrm s[/tex], you get
[tex]d=\dfrac12\left(9.81\,\dfrac{\mathrm m}{\mathrm s^2}\right)\left(2\,\mathrm s\right)[/tex]
[tex]d=\left(4.905\,\dfrac{\mathrm m}{\mathrm s^2}\right)\left(4\,\mathrm s^2\right)[/tex]
[tex]d=19.62\,\mathrm m[/tex]