Ihave attached a picture of a question i am stuck on. it is about riemann sums. i have attempted the question but did not get the correct answer : ( here is my work:

i see that this graph has the same area repeating 12 times.

i did (b - a)/n, or (12 - 0)/36, and found that the width of each rectangle should be 1/3. because we are asked to find the area using "circumscribed angles," i will use right-endpoint rectangles on the first part of the graph that shows a decreasing interval from 0 to 1:

t = 1/3, r(t) = 2.01745506
t = 2/3, r(t) = 2
t = 1, r(t) = 1.45369751

these values for r(t) represent heights of the rectangles. i can add them and multiply by the width of each rectangle:

1/3(2.01745506 + 2 + 1.45369751) = 1/3(5.47115257) = 1.823717523

i can multiply the area by 12 to find the area under the entire function:

1.823717523 * 12 = 21.88461028

this is not an answer choice, so i clearly did something wrong! can someone me find my mistake?