David tunes pianos in his spare time for extra income. buyers of his service are willing to pay $135 per tuning. one particular week, david is willing to tune the first piano for $115, the second piano for $125, the third piano for $140, and the fourth piano for $175. assume david is rational in deciding how many pianos to tune. his producer surplus is

a) $-15.
b) $20.
c) $30.
d) $75.

Look at this pattern ; 1,4,9, number 10000 belongs in this pattern . what’s the place of this number?

Afactory makes propeller drive shafts for ships. a quality assurance engineer at the factory needs to estimate the true mean length of the shafts. she randomly selects four drive shafts made at the factory, measures their lengths, and finds their sample mean to be 1000 mm. the lengths are known to follow a normal distribution whose standard deviation is 2 mm. calculate a 95% confidence interval for the true mean length of the shafts. input your answers for the margin of error, lower bound, and upper bound.

Given the expression (7 ? 4i) ? (2 + 6i), perform the indicated operation and write the answer in the form a + bi.