Formulate the problem as a linear program (define the decisions variables clearly, write the objective function and constraints in terms of those variables.)

Two gasoline types A and B have octane ratings of 80 and 92, respectively. Type A costs $0.83 per liter and type B costs $0.98 per liter. Determine the blend of minimum cost with an octane rating of at least 89.

Hint: The octane rating of the blend equals the sum of the octane rating of each type of gasoline multiplied by its percentage in the blend. For example, a blend of 30% A and 70% B will have an octane level of 0.3(80)+0.7(92) = 88.4 and will cost 0.3(0.83)+0.7(0.98) = 0.935 per liter.