Can someone teach me how to solve equations by using substitution?

my math teacher doesn't explain anything well at all and it causes me to fail every time! it's sad because others understand while i don't. i have homework on the topic but i can't even start!

begin with the basics, i'm completely lost : '(

The value of the expression 16-^3/4 8 1/8 -6 6 1/40 1/64

Determine if the equation defines y as a function of x: 2xy = 1. yes o no

(05.02)a farmer has decided to divide his land area in half in order to plant soy and corn. calculate the area of the entire area so he knows how much soil is needed. a parallelogram with a height of 6 yards and side length 9 yards. the height forms a triangle with the slanted side of the rhombus with a base of 2.5 yards. rhombus is split into a soy half and a corn half. each bag of soil covers 40 square yards. how many bags should the farmer purchase?