3. three friends, named x, y, and z, use the computer every night. regarding the time in hours each person uses the computer per night, it is known that:
- x time minus y time plus z time is 4;
- twice the time of x plus the quadruple of the time of y plus the time of z is equal to 12;
- the time of x equals the sum of the times of y and z. what is the number of hours of computer use by each friend each night? (note: resolve by cramer rule) / (1.0)