Which formula is used to find an object’s acceleration

The equation F=ma where f is force and mass (m) is multiplied by acceleration (a) to get the force. But if you need acceleration, take your force and divide by the mass. Another way to do an equation, for example, is to set up what I like to use called the triangle. Draw one of them, put a line down the middle, and then draw a vertical line across that. In this case, there should be 3 spaces. Force goes on the top, m goes on the next space on the left, then a on the right. Sorry for this long explanation.

t = 1/400 h   ⇔ 0.0025 h ⇔ 9s ⇔ 0.15 m

any of the answers are correct.