given: anglesrt is equivalent to anglestr, m anglesrt = 20, m anglestu = 4x

h

It is given that

 ⇒∠SRT≅∠STR

m∠SRT=20°

So,⇒ m∠SRT=m∠STR=20°{Using (1)]

In ΔSRT

⇒∠SRT+∠RTS+∠TSR=180°Angle Sum Property of Triangle

⇒20°+20°+∠TSR=180°

⇒∠TSR=180°-40°

⇒∠TSR=140°

⇒∠STU=∠TRS+∠RST[Exterior Angle of triangle is equal to sum of it's two interior opposite Angle]

⇒4x=20°+140°

⇒4x=160°

Dividing both side by 4, we get

x=40°

m∠STU=4×40°=160°