The given equation is:
375 = x - 28
To solve the equation:
Collect like terms
The -28 crosses the equality sign to the left and becomes 28
The equation then becomes:
375 + 28 = x
x = 403 (correct answer)
The students error is that when he collected like terms, he did not change the "-" sign in -28 to +
He did 375 - 28 = x
x = 347 (wrong)