Please answer the following questions need help

What is the missing step in this proof ?

Using only odd number for numerators write two different subtraction problems that have a difference of 3/4

Apossible wavelength for the color blue is 0.000000492 meter. which of the following is a reasonable estimate for this wavelength for the color blue? a. 5 × 10-6 m b. 5 × 107 m c. 5 × 10-7 m d. 5 × 106 m