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Give each fruit a letter- apple (a), banana (b), cherry (c), plum (p). Write out each sum using these letters. Find two lines with three of the same fruit and write them as an equation.
eg. 1p+2a+1b+4=1p+1a+1c+1b
simplify the equation
1a+4=1c
repeat this until you have a formula for each fruit
eg. 1b =1c+6
1a=1c+3
1p=1c+7
pick any line and write it out using the formulas
eg. 2c+c+6+c+3=17
simplify the equation and solve for c
4c+9=17
c=2
use this to work out other fruits
c=2, a=5, b=8, p=9