I went through SPSS regression analysis of a certain dataset, tested assumptions, and finally I got a multiple regression model: y=292.953+9.548x_1+14.982x_3+8.907x_5+16.808x_7

Now suppose that next year x_1 is expected to increase by 50% (other assumed to stay the same). I am asked to estimate an effect on y. What is the best way to tackle this problem?

Thank you in advance.