Respuesta :

XxAtomicxX

Step-by-step explanation:

Sn=n/2(2a+(n-1)d). n=20

S20= 20/2 (2x5+(20-1)3 a=5

S20=10(10+57). d=8-5=3

S20=10x67

S20= 670

Hope this helps you

have a great day