18.
-2(-9)+3
18+3
21
Explanation: -2(-9) When multiplying numbers that have both a negative sign, the answer is positive. Multiply normally.
19.
-6(-4)0
24(0)
0
Explanation: -6(-4) As I explained before, the answer would be positive.
24(0) Every number multiplied by 0 is 0.
20.
56+(-7)
49
Explanation: 56+(-7) Any problem like this is just basically going to be 56-7.
21.
-36+(-4)
-40
Explanation: -36+(-4) You are simply adding normally then adding the sign. This will only work if the signs are the same. (Signs are positive and negative.)
For quarters we have:

Where,
x: number of quarters
Clearing x we have:

For nickels we have:

Where,
y: number of nickels
Clearing y we have:

Then, the ratio of quarters to nickels is:

Simplifying we have:

Answer:
The ratio of quarters to nickels in a dollar is:

Answer:
a) 5:3
b) 7.5:5.3
Step-by-step explanation:
150min : 90min (1 and a half hour)
10 : 6
5 : 3
150 × 10 mm : 1060 mm
1500 : 1060
750 : 530
7.5 : 5.3
I’m almost positive that it’s 3