(Originais Teachy 2023) - Question Easy of Mathematics

In a large engineering system, a building is being designed and energy efficiency is a major concern. To ensure the efficiency of heating and cooling, the air conditioning system must be sized according to the specific needs of the building. The engineer in charge of the project must solve a system of linear equations to determine the ideal operating temperatures. Let the following be the system of equations that models the thermal behavior of the building: 2x + y + 3z = 10, 4x - 6y + 8z = 5, 3x + 7y + 5z = 18. The engineer must rewrite this system of equations in the matrix form Ax = b, where A is the matrix of coefficients, x is the vector of unknowns, and b is the vector of constant terms.

João is building a fence for his garden. He decided to make the fence in the shape of a rectangle and already knows that the height is 4 meters and the base is 7 meters. Help João calculate the perimeter of the fence. What is the perimeter of João's garden fence?

João is in a candy store and wants to buy a chocolate bar that costs R$3.50. He hands a R$10.00 bill to the cashier. What is the change amount that João should receive? Select the correct alternative.