This has to do with ratios. If the current width is 8 inches and he wants to have it 35in, you must multiply the length by the same amount to keep it proportional.
45/135 can be simplified to 15/45 by dividing both the numerator and denominator by 3. To get from one fraction the next you multiplied them both by 3. 15 x 3 =45 45 x 3= 135
The area of a parallelogram is just:
A=bh, we are given b=3ft, so b=36in and A=324in^2 so
324=36h dividing both sides by 36
h=9
So the height is 9 inches.
The last part is confusing but how I think it is is you multiply 32 by 2 and subtract 2
