Question

How am I supposed to find ‘t’ here?

Answer 1

You can solve for (T)

$y = - 16t {}^{2} + 400 \\ add \: both \: side \: by \: - 16t {}^{2} \\ - 16t {}^{2} = - 400 \\ divide \: both \: side \: by16 \\ t {}^{2} = - 25 \\ t = \sqrt{25} \\ t = 5 \\ \: also \: it \: can \: be \: - 5 \\ + - 5$

Hope this help :)