What are AC and DC Power respectively used for?

AC changes its direction in regular interval of time while DC is unidirectional flow. Due to many advantages of AC, it used to power our houses and offices while DC is used to power low power devices. AC is easier to transform between voltage levels, which makes high-voltage transmission more feasible

multiple allele inheritance is traits controlled by more than 2 alleles (ex: pigeons having 3 alleles of one gene govern their feather color).

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.