Someone please help me answer this!!

What is the best way to answer questions with a x expression in the question. for example 3x + 10x=?

He weights of 2-pound bags of best dog food are approximately normally distributed with a given mean  and standard deviation  according to the empirical rule, what percentage of the bags will have weights within 3 standard deviations of the mean? 47.5%68%95%99.7%

The distance of a chord from the centre of a circle is 12cm and the lenght of the chord is 10cm. find the radius of the circle