A! You need to multiply all the numbers together
[Edit:}
Okay! So after you have 15+(21)÷3, you have to remember PEMDAS.
PEMDAS is the order in which you solve equations.
1. Parentheses: you solve everything in the parentheses first, all while following the rules of PEMDAS
2. Exponents: after you solve the things in the parentheses, you do the exponents.
3. Then you do Multiplication or Division, solving in the order from left to right.
4. After, you do Addition or Subtraction, solving in the order from left to right.
So using PEMDAS, we'll solve 15+(21)÷3.
We do division before addition, so 21/3 is 7.
Then you add 15 to 7 and get 22 as your final answer.
Hope this helps!
How to get answer by Mimiwhatsup (In Decimal Form):

Answer in Fraction Form: 
Number of pounds of cashews is 36 pounds and number of pounds of walnuts is 4 pounds.
Step-by-step explanation:
- Step 1: Given details are cost of cashews = $1.58, cost of walnuts = 78 cents = $0.78, total weight of nuts = 40 pounds, cost of nuts per pound = $1.50
- Step 2: Let number of pounds of cashews to be mixed be C, then number of pounds of walnuts will 40 - C. Form equation with these variables.
⇒ 1.58 C + (40-C) 0.78 = 40 × 1.50
⇒ 1.58 C + 31.2 - 0.78 C = 60
⇒ 1.58 C - 0.78 C = 60 - 31.2
⇒ 0.8 C = 28.8
⇒ C = 36 pounds
- Step 3: Calculate number of pounds of walnuts
⇒ Number of pounds of walnuts = 40 - C = 4 pounds