Please help and thank you

Solve for n? [tex]z = \frac{3}{4} mn[/tex]

Write the expression 7x^3-28xy^2 as the product of 3 factors

Julie goes to the sports store and spends $40.50 before tax. she buys a pair of shorts for $21.75 and 3 pairs of socks that each cost the same amount. how much does each pair of socks cost? $$