Answer:
[tex]\boxed{6760}[/tex]
Step-by-step explanation:
The formula for the first n terms of an arithmetic sequence is
Sₙ = n(a₁+ aₙ)/2
1. Find the number of terms
n = (124 - 45) + 1 = 79 + 1 = 80
2. Find the sum
a₁ = 45
a₈₀ = 124
[tex]S_{80} = 80 \left(\dfrac{45 + 124 }{2}\right) = 80 \times 84.5= \boxed{\mathbf{6760}}[/tex]
