we will consider the balloons to be spheres

let

r1 = the radius of the smaller balloon

r2 = the radius of the larger balloon

V1 = 50 in^3 the volume of the smaller balloon

V2 = the volume of the larger balloon

V1 = (4/3) r1^3 pi

4/3) r1^3 pi = 50

the dimensions of the larger balloon are twice those of the smaller balloon

r2 = 2r1

V2 = (4/3)( 2*r1)^3 pi

V2 = (4/3)*8*r1^3 pi

V2 = 8*V1

V2 = 8*50

V2 = 400 in^3

the volume of the larger balloon is 400 cubic inches.