She did not give and unknown value for iced tea
you would use 1.5 packets, but that requires 2 packets.
1 packet in total would feed 8 people, and half of another would feed an extra 4. 4+8 = 12.
Given:


Multiply both sides by 3/2, we get

Cancel out the common multiples, we get



The solution of the given equation is

or
Complelment adds to 90
let's say the complement is B
A+B=90
4x+2+B=90
minus (4x+2) from both sides
B=88-4x