Answer:
1) x: small #; y: large #
4y = 7x
x + y = 22
----------------
-7x + 4y = 0
x + y = 22
---multiply the second equation by -4------
-7x + 4y = 0
-4x - 4y = -88
----solve------
-11x = -88
x = 8
---substitute with any of the equation above i chose the very first one------
4y = 7(8)
4y = 56
y = 14
x = 8; y = 14
2) x = small #; y = large #
y - x = 15
5x = y - 9
----after rearranging, solve-----
-x + y = 15
5x - y = -9
-4x = 6
x = -1.5
--------substitute--------
-(-1.5) + y = 15
1.5 + y = 15
y = 13.5
x = -1.5; y = 13.5
3) x = lemon cream; y = fudge cookie
3x + 2y = 400
2x + 3y = 425
----multiply the first equation by -2, multiply the second equation by 3------
-6x - 4y = -800
6x + 9y = 1275
----solve------
5y = 475
y = 95
--------substitute--------
3x + 2(95) = 400
3x + 190 = 400
3x = 210
x = 70
x = 70; y = 95