Question 9517
Let:

x = Cement
y = Gravel

x + y =140

We also know that the cement is 3 times as much as the gravel, so:

x = 3y

So now substitute in the equation x + y = 140 and it becomes: {{{3y+y=140}}}

Combine Terms

{{{4y=140}}}

Divide both sides by 4

{{{y=35}}}

so the Gravel weighs 35 pounds.  We know there is 3 pounds of cement for every pound of gravel, so"

{{{3*35=105}}}

so the cement = 105.

Answer"

35 Lbs. of Gravel
105 Lbs. of Cement