the imo transport company, in order to further enhance its performance is trying to decide whether to purchase brand a or brand b tires for it fleet of vehicle. in order to estimate the difference in the 2 brands. an experiment was conducted using a random sample of 20 tires off brandy and 18 tires of brand b. the result shows that for brand a; X¹=30,500km, S¹=45,000km and for Brand b; X²=27,880km, S²= 3750km. compute a 90% confidence limit for u¹-u², assuming the population to be normally distributed​