One egg and 2 glass of juice cost $2.30. Two egg and 1 juice cost $3.40. What does one egg plus one juice cost?

Simplify the question so it uses x's and y's or any two letters instead of egg/juice (not necessary)

egg = x

juice = y

x + 2y = 2.30

2x + y = 3.40

Make x the subject

x = 2.30 - 2y

Add pervious step to 2x + y = 3.40 then solve for y

2 (2.30 - 2y) + y = 3.40

4.60 - 4y + y = 3.40

4.60 - 3y = 3.40

-3y = - 1.20

3y = 1.20

y = 0.40

Now solve for x

x + 2y = 2.30

x + 2 (0.40) = 2.30

x + 0.80 = 2.30

x = 1.50

One egg costs $1.50

One juice costs $0.40

Therefore, one egg plus one juice costs $1.90