LaTeX: 3\:-\frac{\:2}{9}b\:=\frac{\:1}{3}b \:-\:7

The expression 6x2 gives the surface area of a cube, and the expression x3 gives the volume of a cube, where x is the length of one side of the cube. find the surface area and the volume of a cube with a side length of 6m

Don't know how to find x given these segment lengths

Given the two similar triangles, how do i find the missing length? if a=4, b=5, and b'=7.5 find a'