Construction of the objective function for a mathematical model

Specific Domains Optimization (Mathematical)
4

This is the objective function that I am trying to build.

C1z*(yij+y1ij) + C2z*y1ij

I’m having trouble declaring variables with two indexes in the objective function.

using JuMP, Cbc
Model1 = Model (with_optimizer (Cbc.Optimizer))
C1 = [11; 11; 11; 11; 11]
C2 = [50; 50; 50; 50; 50]

#Sets
i = 80 #activities
j = 18 # time period
z = 5 #work center

#variable
@variable (Model1, y [i, j], lower_bound = 0)
@variable (Model1, y1 [i, j], lower_bound = 0) 

#objective function - wrong function
@objective(Model1,Min,sum(C1[z]*(y[i,j]+y1[i,j])+C2[z]*y1[i,j]) for z ∈ 1:i)