please tell me how to solve below questions (y-axis)

Disk Method

find the volume of the solid obtained by rotating the region bounded by the given equations around the y-axis

a)y=421x,x=0,y=0

b)y=x+11,y=0,x=0,x=2

Washer Method

find the volume of the solid obtained by rotating the region bounded by the given equations around the y-axis

c)y=x+2,y=2x1,x=0

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*For y-axis, a) y=4-1/2x should change to x=-y+4 ?

b) y= 1/x+1 ---> x=1/y-1

c) y= x+2 ---> x=y-2

* I'm not sure how to find points of intersection

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