Are you sure this is written correctly? Any number whose digits add to 9 is divisible by 9. For a 2 digit number then, your choices are
18, 27, 36, 45, 54, 63, 72, and 81. None of these has the property that for the 2 digit number AB that B=2A-1. Solving your question algebraically is possible but you get fractional digits.
1.
- Cone
2.
- Sphere
3.
- Cylinder
4.
- Pyramid
5.
- Prism
Solution:
1. 
Lateral surface area of cone = 
where r is the radius of the cone and l is the slant height of the cone.
2. 
Volume of sphere = 
where r is the radius of the sphere.
3. 
Total surface area of cylinder = 
where r is the radius of the cylinder and h is the height of the cylinder.
4. 
Volume of pyramid = 
where B is the base area of the pyramid and h is the height of the pyramid.
5. 
Lateral surface area of prism = 
where p is the perimeter of the base and h is the height of the prism.
23 is less than 25 which means it's closer to 20, so you would round it down to 20. 1.75 is over 0.50, 1/2, so you would round it up to 2. If you multiply 2 and 20 you would get 40.
Number two gets the same explanation just with different numbers.
Answer:
(-2,-5)
Step-by-step explanation:
y = 2x-1
3x-y = -1
We can use substitution
3x - (2x-1) = -1
Distribute the minus sign
3x -2x+1 = -1
x +1 =-1
Subtract 1 from each side
x+1-1 = -1-1
x=-2
Now we need to find y
y = 2x-1
y = 2(-2) -1
y = -4-1
y = -5
(-2,-5)