Bob sold 5 toaster ovens and 3 blenders for $500. if a blender is $20 less than a toaster oven, how much is a blender?

The answer would be $50 per blender. 
To explain the way I did it --
Toaster ovens - 70 * 5 = 350
70 - 20 = 50
Blenders - 50 * 3 = 150
350 + 150 = 500

The total cost is $500 and this is distributed between 5 toasters and 3 blenders. Let's assign "t" for the price of a toaster and "b" for the price of a blender.
500=5t+3b
we know that a blender costs $20 less than a toaster which is expressed by "b=t-20", so instead of "b" we can write "t-20" to represent the price of a blender
500=5t+3(t-20)
500=5t+3t-60 distribute the 3
500+60=5t+3t-60+60 add 60 to both sides
560=8t add like terms
560/8=8t/8 divide both sides by 8
70=t 
therefore a toaster costs $70
We can then substitute 70 into the "b=t-20" expression to find the price of a blender:
b=70-20
b=50
therefore, a blender costs $50