X/30 + X/40= 1
Solve for x

17 1/7 I think

Step-by-step explanation:

for this case we have that by definition, the surface area of a cylinder is given by:

where:

r: it is the radius of the cylinder

h: it is the height of the cylinder

we can also rewrite it as:

where:

la: it's the lateral area

ba: area of the base

option a

it goes right