Arithmetic progression

In some AP applies:

5a2 + 7a5 = 90
s3 = 12

Find the first member a =? and difference d = ?

Correct answer:

a =  2
d =  2

Step-by-step explanation:

5•(a+d)+7•(a+4•d) = 90
a+(a+d)+(a+2•d) = 12

12a+33d = 90
3a+3d = 12

a = 2
d = 2

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