I have to find the value of each pro-numeral, and show the steps of working.

I know it's an isosceles, and it's exactly like a traingle except it's on it's side, and it's pointing right.The bottom angles < > left and right are the pro-numerals b, and where the sides come up to meet the tip (top) the sides are equal, and the right side, near the tip, is 40*

How would i find the angle of the pronumerals??