Answer: (0.00306,0.00334)
Step-by-step explanation:
Given : Sample size : n= 420000
The number of users developed cancer of the brain or nervous system =134
Then , the proportion of users developed cancer of the brain or nervous system :

Significance level : 
Critical value : 
The confidence interval for population proportion is given by :-

Hence, the 90% confidence interval estimate of the percentage of cell phone users who develop cancer of the brain or nervous system is (0.00306,0.00334).
The triangle is isosceles, so the bottom angles have the same measure. So, the angles measure 2x, 3x+5 and 3x+5.
The sum of the interior angles of a triangle is 180, so we have

So, angle A measures
