Answer :
Selina and cooper with both have $40 in their bake account at the same time in month 3 with Selina adding $10 each month and Copper taking $20 away each month.
STEP-BY-STEP
Month 1. Selina- adds $10= $20
Month 1. Cooper- takes $20= $80
Month 2. Selina - adds 10=$30
Month 2. Cooper- takes $20= $60
Month 3. Selina- adds $10= $40
Month 3. Cooper-takes $20= $40
STEP-BY-STEP
Month 1. Selina- adds $10= $20
Month 1. Cooper- takes $20= $80
Month 2. Selina - adds 10=$30
Month 2. Cooper- takes $20= $60
Month 3. Selina- adds $10= $40
Month 3. Cooper-takes $20= $40