53 times .07 is 3.71
53 times .15 is 7.95
You add those and get $64.66.
Error = 1/2(Maximum range - Minimum range) = 1/2(3.2-1.1) = % = 0.0105
If p is the point estimator;
Then,
Minimum range = p - Error
Maximum range = p + Error
Solving one of the two expressions,
0.011 = p - 0.0105 => p = 0.011+0.0105 = 0.0215 = 2.15%