To isolate x, use opposite operations.
4.2 is added to x. So, to get x by itself, subtract 4.2.
To keep the equation balanced, subtract 4.2 from both sides of the equation.

x + 4.2	=	5
x + 4.2 − 4.2	=	5 − 4.2
x	=	5 − 4.2
x	=	0.8

To isolate x, use opposite operations.
x is multiplied by 4. So, to get x by itself, divide by 4.
To keep the equation balanced, divide both sides of the equation by 4.

4x	=	20
4x ÷ 4	=	20 ÷ 4
x	=	20 ÷ 4
x	=	5

The commercial aired four times each hour for h hours.
The commercial aired 12 times in those h hours.
So, h groups of four equals 12.

4h	=	12
4h ÷ 4	=	12 ÷ 4
h	=	3

Note that other equations in the same fact family could also be used to solve for h.

Shelly has $4\frac{1}{3}$ yards of fabric.
She needs an additional f yards of fabric to have a total of 6 yards of fabric.

Note that other equations in the same fact family could also be used to solve for f.

To isolate x, subtract 4.2 from both sides of the inequality.

x + 4.2	≥	5
x + 4.2 − 4.2	≥	5 − 4.2
x	≥	5 − 4.2
x	≥	0.8