How to tell if a function is differentiable on an interval?

What are the solutions of the equation? 6x^2 + 11x + 4 = 0 a. 4/3, 1/2 b. -4/3, -1/2 c. 4/3, -1/2 d. -4/3, 1/2

The annual snowfall in a town has a mean of 38 inches and a standard deviation of 10 inches. last year there were 63 inches of snow. find the number of standard deviations from the mean that is, rounded to two decimal places. 0.44 standard deviations below the mean 2.50 standard deviations below the mean 0.44 standard deviations above the mean 2.50 standard deviations above the mean

The perimeter of a rectangle is 42 inches. if the width of the rectangle is 6 inches, what is the length