Please help with c&d, I keep getting the answer incorrect.

(14%) Problem 7: A small block of mass M = 950 g is placed on top of a larger block of mass 3M which is placed on a level frictionless surface and is attached to a horizontal spring of spring constant k = 6.6 N/m. The coefcient of static friction between the blocks is ,u. = 0.2. The lower block is pulled until the attached spring is stretched a distance D = 4.5 cm and released. Randomized Variables M: 950 g D: 4.5 cm k = 6.6 N/m 25% Part (:1) Assuming the blocks are stuck together, what is the maximum magnitude of acceleration am of the blocks in terms of the variables in the problem statement? amm=(k)(D)/(3 M+M) \"Correct! 25% Part (b) Calculate a value for the magnitude of the maximum acceleration am of the blocks in 111/52. em\" = 0.0?310 t/ Correct! $3 25% Part (c) Write an equation for the largest spring constant km for which the upper block does not slip. kmm = ( p. M g )r'( D ) X Feedback: Your answer was offby a factor of 1J4. Please check your calculations. $3 25 \"Va Part (d) Calculate a value for the largest spring constant km for which the upper block does not slip, in Nr'm. Grade Summary kmwt = 413' Deductions Potential 100 'Fo Submissions Attempts remaining: 7 (_ per attempt) detailed View 1 2 Degrees O Radians - 3 Submit Hint l 1 give up! Hints: deduction per hint. Hints remaining: i Feedback: deduction per feedback