Answer:
u = 23°
Step-by-step explanation:
[tex]2u + u + {21}^{o}= {90}^{o} \\3u + {21}^{o} = {90}^{o} \\ 3u = {90}^{o} - {21}^{o} \\ 3u = {69}^{o} \\ u = \frac{ {69}^{o} }{3} \\ u = {23}^{o} \\ [/tex]
