Marsha should specialize in cooking cakes because she can bake cakes faster.
PROOF that she can bake cakes faster
5cakes in 60minutes--in fraction form is 5/60 reducing in the fraction shows that Marsha can cook 1 cake in 12 minutes. while Howard 3/60 can only bake 1 cake in 20.
Howard should specialize is Pizza because he cook pizzas faster than Marsha.
PROOF(same concept as last)
Marsha 10/60->1/6= 1 pizza in 6 minutes
Howard 12/60->1/5= 1 pizza in 5 minutes