The missing first letter is which

Data on oxide thickness of semiconductors are as follows: 426 432 418 418 421 436 418 408 431 435 423 426 411 434 435 432 411 426 407 439 422 426 412 416 consider this data as a sample of the population. (a) calculate a point estimate of the mean oxide thickness for all wafers in the population. (round your answer to 3 decimal places.) (b) calculate a point estimate of the standard deviation of oxide thickness for all wafers in the population. (round your answer to 2 decimal places.) (c) calculate the standard error of the point estimate from part (a). (round your answer to 2 decimal places.) (d) calculate a point estimate of the median oxide thickness for all wafers in the population. (express your answer to 1 decimal places.) (e) calculate a point estimate of the proportion of wafers in the population that have oxide thickness greater than 430 angstrom. (round your answer to 4 decimal places.)