The equation for distance is d = st. if a car has a speed of 77.0 m/s and travels for 45.0 seconds, how far does it go?

The equation is  d = s t , just like it says right at the beginning there.

-- Take the equation.

-- In the place where the equation says "s", erase 's' and write "(77 m/s)".

-- In the place where the equation says "t", erase 't' and write "(45 sec)".

-- NOW the equation says  d = (77 m/s) (45 sec) .

-- When there are two numbers right next to each other like that,
it means you're supposed to multiply them.

-- So multiply them.

-- Their product is equal to "d", and that's the answer.