plz explain how to do this in detail:

Question

using only 39 cent and 24 cent stamps, charlie put $7.14 postage on a package he mailed to his sister. if he used twice as many 39 cent stamps as 42 cent stampsp, how many 24 cent stamps did he use??

Answer 1

first represent the unknowns using variables:
let x = number of 24-cent stamps used
let 2x = number of 39-cent stamps used (according to the second statement)
since the total is 7.14 dollars,
0.24x + 0.39(2x) = 7.14
now we solve for x:
0.24x + 0.78x = 7.14
1.02x = 7.14
x = 7 (number of 24-cent stamps used)

hope this helps~ :)

Answer 2

Triple a number plus 7 results in 16. What is the number?

Answer 3

let x = number
according to the first statement, we multiply the number by three, then we add 7 to get 16,, writing in equation:
3x + 7 = 16
now solve for x,, first we transpose the 7 on the other side of equation,, to do this we change its sign from positive to negative:
3x = 16 - 7
3x = 9
to get x alone, we divide both side of equation by 3:
(3x)/3 = 9/3
x = 3

hope this helps~ :)