1.75=12.3-x/2.8 i tried to solve but said answer is 7.4

The answer is 7.4.
First you have to multiply 1.75 by 2.8 which is equal to 4.9. After that you have to subtract 12.3 to other side because you want the variable by itself which is x. So subtract 4.9 by 12.3 and you get -7.4. No you have something like this: -7.4 = -x. Now you have to divide by negative 1 and you answer is positive 7.4 because when you divide by two negative number the answer is always positive. So x = 7.4 

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The answer is correct