Solve for :
Collapse the nested brackets first. The inner expression contains only constants and one :
so the equation becomes
Doing this before distributing keeps the from being multiplied across three terms instead of two.
Distribute the across both terms.
Note , and it is subtracted because the whole bracket is subtracted.
Combine like terms on the left. The terms give , and the constants give :
The coefficient is the readable meaning of the problem: of the excess is taken away, so of survives.
Isolate the term. Add to both sides:
Divide by carefully.
Converting to the exact fraction before dividing is the safest way to get the digits right; the nearby wrong value comes from a single mis-carried digit in the long division.
Check by substituting back. With : the bracket is , times is , so the left side is ✓. (Using instead would give , one whole unit off.)
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