Answer:
83
Step-by-step explanation:
70=x-13
70+13=x-13+13
83=x
12 bikes
9 tricycles
x+y=21
2x+3y=51
x=-y+21
2(-y+21)+3y=51
-2y+42+3y=51
y+42=51
y=9
x=12
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