If you only want the dual you don`t need to use any solver
using JuMP, Dualization
FabricaBrinquedos = Model()
L = [12 ;60]
T = [0.25 0.1 0.1; 0.5 0.75 0.4]
D = [36; 22; 15]
@variable(FabricaBrinquedos, X[i=1:2] >= 0)
@objective(FabricaBrinquedos,Max, sum(L[i]*X[i] for i=1:2))
@constraint(FabricaBrinquedos, con[j in 1:3], sum(X[i]*T[i,j] for i=1:2) <= D[j])
print(FabricaBrinquedos)
dual_model = dualize(FabricaBrinquedos, dual_names = DualNames("", ""))
print(dual_model)
This code got me this
julia> print(dual_model)
Min -22 con[2]_1 - 15 con[3]_1 - 36 con[1]_1
Subject to
X[1] : 0.25 con[1]_1 + 0.1 con[2]_1 + 0.1 con[3]_1 + _1 = -12.0
X[2] : 0.5 con[1]_1 + 0.75 con[2]_1 + 0.4 con[3]_1 + _1 = -60.0
_1 ≥ 0.0
_1 ≥ 0.0
con[1]_1 ≤ 0.0
con[2]_1 ≤ 0.0
con[3]_1 ≤ 0.0