<span>d = 5x + 5y
5y = d - 5x
y = (d - 5x) / 5</span>
The other person did not explain so I will:
(68+79+74)= 221/3 =73.7
80 x 4 = 320
320-221 = 99
He must get 99 on his 4th test.
Thanks
x = longer section
y = shorter section
x + y = 109
x = 2y + 10
so we sub in eq 2 into eq 1
2y + 10 + y = 109
3y + 10 = 109
3y = 109 - 10
3y = 99
y = 99/3
y = 33 <=== shorter section is 33 cm
x = 2y + 10
x = 2(33) + 10
x = 66 + 10
x = 76 <=== longer section is 76 cm