Question 514129
2 pieces:  x, y
x+y = 81
.
x = 3y -7
.
substitute
.
3y-7 +y = 81
.
4y = 88
.
y = 22
.
x = 3(22)-7
x = 66-7
x = 59
.
Check the solution.
22+59 = 81
OK.
.
Answer the two pieces are: 22 and 59 cm.