Sound Waves? A. are a part of the electromagnetic spectrum
B. do not require a medium for transmission
C. are longitudinal waves
D. are transverse waves

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form

force required to detach it is given by

charges are taken to be fundamental charge

now we have

so above is the minimum distance at which it will detach