Let's see if I remember this......!!!!!
sin 45 / 13.5 = sin B ' / 18
sin B' = (18/13.5) sin 45
Take the sine inverse
arcsin [ (18/13.5) sin 45 ] ≈ 70.53....°
But this angle is obtuse....so....its measure = 109.47°
And since we have an isosceles triangle on the right
Then angle B is supplemental to 109.47 ≈ 70.53°
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