n=i*x+y for i

[math_celebrity]

n=i*x+y for i

This is a literal equation.

Subtract y from each side of the equation:
n - y = i*x + y - y

The y's cancel on the right side, so we have:
n - y = ix

Divide each side of the equation by x, to isolate i
(n - y)/x = ix/x

The x's cancel on the right side, so we have:
i = (n - y)/x