Easy

Answer: 15
Solution:
If you see there are 3 variables and 3 equations, we can solve the equations and get the variables values and than we can find the value of fourth equation.

From the first equation we can say that ColdDrink = 10
than from the second Burger = (20 – 10)/2 = 5
and from the third equation FrenchFries= (9 – 5)/4 = 1

Thus Burger + FrenchFries * ColdDrink = 5 + 1*10 = 15

here as per BODMAS 5 + 1*10 will be 5 + 10 = 15

-1^n is 1 (if n is even) OR -1 (in n is odd)

but in this equation power is on 1 not -1
-1¹²¹-1¹²² -1¹²³-1¹²^⁴ = -1-1-1-1 = -4