How to solve for di? Equation: 1/f = 1/do + 1/di

People are saying find the common denominator but I don’t understand how to.

Choose all answers that apply: a) ab and a’b’ are one the same line. b) quadrilaterals abcd and a’ b’ c’ d’ have the same perimeters. c) points a and a’ have the same coordinates. d) none of the above

After applying the composition r0.90 ry to rs what are the coordinates of r' and s'? a. r'(–3, 1),  s'(–3, 5)b. r'(–1, 3),  s'(–5, 3)c. r'(1, 3),  s'(5, 3)d. r'(5, 3),  s'(1, 3)

What is the value of x in the equation 1.5x+4-3=4.5(x-2)?