on the attachment, there is the graph for the region "R" and the calculations for the value a and b.
the theory is that you have to choose a value that is between the range and assume that this value will divide the area into two equal parts. This is done for x = a
For
"y" you have to change the integral from dx to dy and you have to divide the region into 2 parts, given that the area cannot be calculated by 1 integral equation, so you proceed to calculate the rectangular area and take this area into consideration, for the same procedure as before.
Then you calculate again the value y = b and that's it.