Any math experts in geometry on coordinates...??Please help thx

Answer:
green box= b
grey box = a
Step-by-step explanation:
They are asking for the distance formula for RS.
d = √(x2-x1)² +(y2-y1)²
(0,a) is x1, y1
(b,c) is x2, y2
d= √(b-0)² + (c-a)²
d = √(b)² + (c-a)²