Start with the question you want to answer: "How many washing machines did the company import?"
Let x be the number of washing machines imported. The goal is to find the value for x.
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The company was able to sell one third of the imported machines. So they sold (1/3)x = x/3 machines and are left with (2/3)x = 2x/3 machines.
Then they sell another 10 machines. So the count 2x/3 will drop by 10 meaning we now have 2x/3 - 10 machines left.
We are told that there are half of the machines imported left over, so there are (1/2)*x = x/2 machines left over.
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Equate 2x/3 - 10 and x/2, then solve for x
2x/3 - 10 = x/2
6*(2x/3 - 10) = 6*(x/2) ... multiply both sides by 6 to clear the fractions
6*(2x/3) + 6(-10) = 6*(x/2) ... distribute
4x - 60 = 3x
4x - 60+60 = 3x+60 ... add 60 to both sides
4x = 3x+60
4x-3x = 3x+60-3x ... subtract 3x from both sides
x = 60
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Answer: The company imported 60 washing machines.
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As a check, let's divide this by 3 to get 60/3 = 20. The company is able to sell 20 machines at first (that batch where they sold one-third of the amount they imported). Then they sell 10 more machines to sell 20+10 = 30 machines overall. If they started off with 60 machines and sold 30 of them, then they have 60-30 = 30 machines left which is half the initial batch (because 30/60 = 1/2). This is one way to confirm the answer.
Another way to check the answer to plug x = 60 into 2x/3 - 10 = x/2 and you should get the same number on both sides after you simplify. I'll let you do this as practice.