How fast does this outer layer move usually?

On average, at about the rate that fingernails grow, approximately 3-4 cm per year. This is variable, however, often even across an individual plate, from between 1-2 cm per year for the slowest moving plates to around 10 cm per year for the fastest.

angle a = 40.6°

step-by-step explanation:

for any right angle triangle we know the pythagoras theorem reveals

hypotenuse² = height²+base²

by this formula we will calculate the length of hypotenuse

h² = 6²+7²

⇒ h =√36+49 = √85 = 9.22

now from the given triangle sin a = height/ hypotenuse

                                                sin a = 6/9.22 = 0.651

therefore

so angle a = 40.6°

doesn't make any since

explanation: