Answer:
1) She earn $1600 by selling her 2000 muffins on both days.
2) The amount of money boys have altogether in the beginning is $180.
Explanation:
1) Given : Mrs. Rothberg baked 500 muffins on Saturday and 3 times as many muffins on Sunday. If the sold 5 muffins for $4.
To find : How much would she earn by selling her muffins on both days?
Solution :
On Saturday she manufacture = 500
On Sunday she manufacture =

Total manufacture on Saturday and Sunday is

She sold 5 muffins for $4.
She sold 1 muffin for
.
She sold 2000 muffin for
.
She sold 2000 muffin for $1600.
Therefore, she earn $1600 by selling her 2000 muffins on both days.
2) Given : Jack had $80 more than Eric. When Jack spent $30, he found that the amount of money he had left was twice as much as what Eric had.
To find : How much did the boys have altogether in the beginning?
Solution :
Let amount of money Jack has 'x'.
The amount of money Eric has 'y'.
According to question,
Jack had $80 more than Eric.
.....(1)
When Jack spent $30, he found that the amount of money he had left was twice as much as what Eric had.
.....(2)
Substitute the value of x in (2),


Substitute in equation (1),


The amount of money the boys have altogether in the beginning is

Therefore, the amount of money boys have altogether in the beginning is $180.