$\mathbf Question.$ A stone projected vertically upwards with initial speed of $u\ m/s$ rises $70\ m$ in the first $t$ seconds and another $50\ m$ in the next $t$ seconds.
$\bullet$Find the value of $u$ and $t$.
$\mathbf Attempt.$ I have tried simultaneous equation with $s=ut+.5at$ $$70=u(t)+(.5)(-9.8)(t)^2$$ $$120=u(t+1)+(.5)(-9.8)(t+1)^2$$ Since $v=u+at$I also let: $$t= \frac{-u}{-9.8}$$
In the end I got $u =49.5$and $t=5$
But that isn't the answer at all so what am I doing wrong?