Step 1: Recall the standard form of a linear equation in two variables
A standard form of a linear equation in two variables is in the form ax+by = c
Step 1: Assume one piece of cable to be x and the other piece of cable to be y
Step 2: Write the first linear equation as x+ y = 84
Step 3: Assume x to be 18 metres longer than y
Step 4: Write the second linear equation as x = 18 +y
Step 5: Use the substitution (easy) method, write both the equations in x = form or y = form
x = 84 -y
x = 18 +y
Step 6: Write them across each other
84 - y = 18 +y
Step 7: Solve for y
84 - y = 18 + y
2y = 102
y = 51
Step 7: Substitute the value of y in any one of the equations to find the value of x
x = 84 - 51 = 33
So the length of one piece of cable is 33 m and the length of the other piece of cable is 51m