Answer:
no solution (either equation)
Explanation:
2.a 21x +15y = 61 . . . . has no solution in integers
The left side is a multiple of 3; the right side is prime. No multiple of 3 will be a prime number.
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2.b subtracting 6 from both sides and dividing by 2 gives ...
11u +72 = 0
72 is not a multiple of 11, so there can be no integer value of u that satisfies this equation.
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Neither equation has an integer solution.