How do I figure out these questions?
Could you please teach me and give me examples? Examples with the answer and why it is would also be appreciated!

1) How tall are Sally and Anna if Sally is 0.1 m taller than Anna and their combined height is 3.16 metres?
Sally _ Anna _

2) Find these simple quantities
a. 1/5 of $50
b. 10% of $40

Thank you!