Wires in an circuit, different materials, heat

[Regla]

Homework Statement

In an electric circuit, consisting of copper wires with cross section area of S_c=5mm² and a temperature of t=25C, a lead fuse is added melting when the copper wire temperature increases by Δt=25C. Find the cross section area of the lead fuse wire S_l=x.
specific heat: c_c=400J/kg*C c_l=140J/kg*C.
Lead melting point t_l=327C, latent heat λ=25000J/kg.
Specific electrical resistances of the materials: ρ_c=0,017*10^-6Ωm, ρ_l=0,21*10^-6Ωm.
material density: ρ_c1=8,9*10³kg/m³, ρ_l1=11,34*10³kg/m³.

Homework Equations

Q=cmΔt
Q=λm
R=lρ/S

Thank you for any ideas on how to solve this, if there is something confusing please ask, this equation is translated from a different language so there may be inaccuracies and such.

 

[BvU]

Don't erase the part 3. Attempt at solution. We can't help if you don't post that...

 

[Regla]

I was asking for ideas, directions to try going towards, I'm not asking people to solve it. Anyway, I was thinking about Q₁=Q₂ Q₁=c_cm1Δt Q₂=c_l(t_l-t). But I don't know the masses nor anything derivative from it since I need to find the cross section area.