a is the number of pounds of apples
b is the number of pounds of bananas
Apples cost: 2a
Bananas cost: b
As Tony has $18 to buy apples and bananas the inequality that represents the situation is:

To graph it:
1. Identify the equation of the boundary line:

2. Find two ordered pairs:
Find b when a is 1:

Ordered pair: (1,16)
Find b when a is 3:

Ordered pair: (3,12)
2. Use the ordered pairs to draw the boundary line, as the inequality sing is less than or equal to shadow area is under the line:
The possible combinations of pound of apples and bananas are those combinations that fits in the shadow area.