9/2 = x/8
first you cross multiply
9 * 8 = 2 * x
9 * 8 = 72 = 2 * x
72 = 2x
now add -2x to each side of the equation
72 + -2x = 2x + -2x
now combine like terms
2x + -2x = 0
72 + -2x = 0
now add -72 to each side
72 + -72 + -2x = 0 + -72
combine like terms
72 + -72 = 0
0 + -2x = 0 + -72
-2x = 0 + -72
combine like terms
0 + -72 = 0
-2x = -72
divide each side by -2
x = 36
now for the letter b one
4/b+2 + 2/7
cross multiply
4 * 7 = b + 2 *2
4 * 7 = 28
28 = b + 2 * 2
now you gotta reorder the term
28 = 2 + b * 2
28 = 2 * 2 + b * 2
28 = 4 + 2b
solving for the variable b
28+ -2b = 4 + 2b + -2b
combine like terms
2b + -2b = 0
28 + -2b = 4 + 0
28 + -2b = 4
now add -28 to both sides
28 + -28 + -2b = 4 + -28
28 + -28 + 0
-2b = 4 + -28
combine like terms
4 + -28 = -24
-2b + -24
now divide each side by -2
b = 12