Tom and Shondra can complete a job working together in 5 hours this their together rate is 1/5 of the job per hour

Shondra takes 7 hours to do the job alone thus her rate is 1/7 of the job per hour

let x = the hours Tom needs to complete the job alone

The rate of Tom is 1/x jobs per hour

Now we have:

1/7 + 1/x = 1/5

by solving we find:

x = 17.5 h

click here to see the step by step solution of the equation:

Tome needs 17.5 hours to complete the job alone.