Start by naming things. Since you are asked for the numbers of each type of plane, pick variables to stand for these unknowns.

x: number of 747s

y: number of 777s

z: number of A321s

You are given a relationship between the types of planes, the cost of one of each, and the total spent. Use this relationship to create an equation.

You are given a relationship between the types of planes, the seating in one of each, and the total seating ordered. Use this relationship to create an equation.

You are given a relationship between the total number of 747s and 777s and the number of A321s. Use this relationship to create an equation.

You now have three equations in three unknowns. Solve the system for the values of the variables.

The second exercise works similarly. If you get stuck on either, please reply showing what you have tried and how far you have gotten. Thank you!