These questions are worded absolutely terrible bro, are you sure you copied them down correctly? This is why no one is answering you...
1. So he receives a $3 raise each day? Why not just say that in the question lol.
Anyway to be thorough to find out how much the "certain amount" is each day, let Ss=Starting Salary, S= Salary on Specific Day, D=Days (after his first day), A=Amount,
So to put it into words and to help you visualize, his Salary on Specific Day is equal to an Amount multiplied by Days, plus his Starting Salary.
S = DA + Ss would be your equation. What information do we have? Well, we know Salary on Third Day = 18$, Days = 2, Starting Salary = $12, the unknown is the Amount, A
$18 = (2 Days)(A) + $12 //Subtract $12 from both sides:
$6 = (2 Days)(A) //Divide both sides by 2 days
A = $3/Day
2. Assuming he received a raise each day of the amount of $3, we can use the same equation we created above. This time, however, we are missing the "S" Salary on Specific Day Variable.
S = DA + Ss //Where D = 16 days, A = $3, SS = $12
S = (16 days)($3/day) + $12
S = $48 + $12
S = $60
3. Fastest way to do this is to take an average. So, we want to know what was the average pay that was taken home between day 1 and day 22? So, we already know that the salary for Day 1 = Ss = $12. Now we need to find the salary for day 22. Let's plug it into our equation:
S = (21 Days) ($3/day) + $12
S = $75
So, now we know that on day 1 he made $12, and on day 22 he made $75. So, to find the average pay, we sum up $12 and $75, and divide by 2.
$75+$12 = $87;
$87/2 = $43.50.
So we know that, on average, he made $43.50 every day that he worked. He worked for a total of 22 days. To find out how much was made in total, multiply $43.50/day x 22days to get $957.
Hope this helps, I tried to be as thorough as possible and explain in basic, intuitive terms.