Question 27999
Acceleration is equal to change of velocity divided by change of time. The formula is written 
{{{(V2-V1)/(T2-T1)}}} So if your initial velocity (V1) is 0 and you accelerate up to 54 mph (V2) and it takes 5 seconds then you go from an initial time T1=0 to T2=5. Put into the equation:
{{{(54-0)/(5-0)=54/5=10.8}}} mph per second.

Problem 2:  Distance = speed x time. To solve for time, divide both sides by speed to get Distance/Speed = Time.  In a simpler example, if you're doing 50 mph (speed) and went 150 miles (distance) you'll have traveled 150/50=3 hours. In your problem we have a speed {{{3*10^8}}}m/s and a distance {{{149*10^9}}}m so our time is:
{{{149*10^9/(3*10^8)=1490/3=497}}}seconds.