for a normal triangle its (bh)/2 but this is a right triangle so you multiply the two perpendicular sides and divide it by 2
divide total paid by number of pencils for price of 1 pencil
4.50 / 18 = 0.25 for 1
so you would put a dot at (1, 0.25) (2,0.5) (3,0.75) etc and draw a line through the dots
see attached picture:
Should be the right answer ☺️
2x+1=13 x=6 so an ok answer would be: 2x+10=40 x=15