Answer:    y= 40
Step-by-step explanation:
Given : An isosceles triangle ABC.
∠A = (2y+20)°  
∠B= (5x)°
∠C = 40°  
Also, it is given that Sides AB and AC are equal. 
⇒ ∠B = ∠C  [∵ angles opposite to equal sides of a triangle are equal.]
⇒ ∠B  = 40°
[tex]\Rightarrow\ 5x=40\\\\\Rightarrow\ x= \dfrac{40}{5}=8[/tex]
So the value of x= 8
Using Angle sum property of triangle , we have
∠A+∠B+ ∠C=180°
⇒ (2y+20)°  +40°+40°=180°
⇒ 2y+20+ 40+40=180
⇒ 2y+100=180
⇒ 2y =180-100 =80
⇒ y =40 [divide both sides by 2]
Hence, the value of y= 40