Answer:
b = 18
The mortar is 17 times ( 3 / 8 ) tall.
The brick height is equal to 18 times ( 2 + ( 1 / 4 ) ).
I don't know the options, so you have to use those values.
Step-by-step explanation:
Deciphering
The question uses imperial units which are generally bad.
12 inches = 1 feet;
The height of the wall should be written in inches for convenience.
4 feet = 4 * 12 inches;
4 feet = 48 inches;
The wall is short 1 + ( 1 / 8 ) inches short of 4 feet.
48 inches - ( 1 + ( 1 / 8 ) inches ) = 46 + ( 7 / 8 ) inches;
Now that the wall is done let's do the bricks. The height of the bricks is 2 + ( 1 / 4 ) inches and the mortar is ( 3 / 8 ) inches tall. The amount of mortar is the number of bricks - 1 because nobody puts extra mortar on the top of the wall.
Algebra
let b;
46 + ( 7 / 8 ) = b( 2 + ( 1 / 4 ) ) + ( b - 1 )( 3 / 8 );
375 / 8 = b( 9 / 4 ) + ( 3 / 8 )b - ( 3 / 8 );
375 / 8 = ( ( 9 / 4 ) + ( 3 / 8 ) )b - ( 3 / 8 );
375 / 8 = ( ( 18 / 8 ) + ( 3 / 8 ) )b - ( 3 / 8 );
375 / 8 = ( 21 / 8 )b - ( 3 / 8 );
Multiply both sides by 8 to get rid of those annoying fractions.
375 = 21b - 3;
Add 3 to both sides.
378 = 21b;
Divide both sides by 21.
18 = b;