If we have 24+37=7 and 12+18=3 , then find out 54+21 equals?

Give chapter 5 lines and angles own questions for board exams 

Find the following percentage value:

1) 15% of 250.

Find the angle which is equal to its supplement.

Find the breadth of the rectangle whose length is 70 cm and perimeter 200 cm.

Convert 1 gallon into liters.

a. 3.05 liters

b. 3.78 liters

c. 4.05 liters

d. 4.78 liters