4x + 5y = 60 pounds (1)
2x + 4y = 42 pounds (2)
To solve this system, multiply eq(2) by 2 (both sides). Keep eq(1) as is. You get
4x + 5y = 60 (3) (same as (1) )
4x + 8y = 84 (4)
Now subtract eq(3) from eq(4) (ELIMINATION method !). You get
3y = 24 =================> y = 24/3 = 8 pounds is the weight of one (of each) monitor. ANSWER
Then from eq(1) x = = 5 pounds is the weight of one (of each) computer. ANSWER