In the following problem, '=' stands for '÷' , '+' stands for '' , 'x' stands for '=', '' stands for '+' and '÷' stands for 'x'. Find the correct equation.
Calculate a country's GDP if for the year, consumer spending is $400 million, government spending is $150 million, investment by businesses is $80 million, exports are $35 million and imports are $40 million.