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Let x be his saving in November (exactly the unknown value).
Then his saving in December was 0.5x, according to the condition.
Thus his November salary is 1600 + x dollars;
his December salary is 1600*1.3 + 0.5x dollars.
The salary is the same -- it gives you an equation
1600 + x = 2080 + 0.5x
Simplify and solve it :
x - 0.5x = 2080 - 1600
0.5x = 480
x = = 960.
ANSWER. His November saving was 960 dollars.
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You can solve the problem MENTALLY, too, i.e. without using equation/equations.
He increased his spending by 1600*0.3 = 480 dollars, and, therefore (or due to it), he decreased his saving in half.
Hence, half of his saving in November is exactly 480 dollars -- thus his saving on November was 2*480 = 960 dollars.
You get the same result.