Help me solve this problem please

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

Find the maximum value of p= 4x + 5y subject to the following constraints :

Serena is making an experiment. for that, she needs 20 grams of a 52% solution of salt. she has two large bottles of salt water: one with 40% and the other with 70% of salt in them. how much of each must she use to make the solution she needs? i am in need of