Use PEMDAS
P Parentheses first
E Exponents (ie Powers and Square Roots, etc.)
MD Multiplication and Division (left-to-right)
AS Addition and Subtraction (left-to-right)

Answer:
Step-by-step explanation:
If you meant to type x+1<21, then we simplify this inequality by subtracting 1 from both sides, ending up with x < 20.
I do not recognize what your "4" represents.
Answer:
6 x y
Step-by-step explanation:
Expanded
Or add y 6 times
y + y + y + y + y + y
Subtract the amount you have from the amount you need:
2 cups - 1 3/8 cups
Subtract the whole cup first:
2 cups -1 cup = 1 cup
8/8 = 1
Rewrite 1 as 8/8 then subtract the 3/8 you have:
8/8 - 3/8 = 5/8
You need 5/8 cup more
Answer:
$ 78.78
Step-by-step explanation:
Calculate 15% of 68.50. then add it to the total bill.