請問有冇人識以下的數?

請問有冇人識以下的數?
A君用31元買了4個蘋果及5個梨, B君用32元買了5個蘋果及4個梨, 如果買1個蘋及1個梨要多少錢? 請將算式列出!!!!!!!!!

ans:
4X+5Y=31
5X+4Y=32

9X+9Y=63
X+Y=7

X = apple and Y = pear.

31 = 4a+5p ----- (1)
32 = 5a+4p ----- (2)
a+p = ?

(2) - (1) :

1 = a - p
a = p + 1 ----- (3)

Sub. (3) into (2) :
32 = 5(p+1)+4p
32 = 9p+5
p = (32-5)/9 = 27/9 = 3
a = p+1 = 3+1 = 4

買1個蘋及1個梨要(a+p) = 3+4 = 7元

let x=蘋果,y=梨
4x+5y=31-----------(1)
5x+4y=32-----------(2)

(1)*5 20x+25y=155
(2)*4 20x+16y=128

20x+25y=155
-20x+16y=128
9y=27
y=3

put y=3 into (1)
4x+5(3)=31
4x=16
x=4

所以1個蘋果要4元，1個梨要3元

system:

4X+5Y=31
5X+4Y=32

9X+9Y=63
X+Y=7

X = apple and Y = pear.

let A=蘋果, B=梨
4A+5B=31
5A+4B=32
將兩式相加
9A+9B=63
9(A+B)=63
A+B=63/9=7

let x=蘋果, y=梨
4x+5y=31
5x+4y=32

9x+9y=63
x+y=6