Lets get started :)
We need to isolate t from x =

at²
Take 2 to the left-hand side { Do multiplication since you see division }
2x = at²
Take a to the left-hand side { Do division since you see multiplication }

= t²
Take square root since t is to the power of 2

= t
70 x 3 I think cuz that's what I think j learned sorry if it's wrong
Multiplying 20×1/2 is the same as dividing 20 by 2. Which means the answer is 10.
Round 28 to nearest ten and 868 to nearest hundred
900 ÷ 30 = 30