Question

378 + 97 = 378 + 100 -

Explanation:

Step1: Simplify the right - hand side

$378 + 100=478$

Step2: Rewrite the equation

The original equation $378 + 97=378 + 100-\square$ becomes $475 = 478-\square$.

Step3: Solve for the unknown

$\square=478 - 475$
$478-475 = 3$

Answer:

$3$