# Looks tough! [part 3]

**Algebra**Level 4

\[ \large 1 + 4x + 7x^2 + 10x^3 + \cdots = \dfrac{35}{16}\]

Find the value of \(x\) satisfying the equation above. If \(x\) is in the form of \(\dfrac ab\) where \(a\) and \(b\) are positive integers with \(\gcd(a,b)=1\), submit your answer as \(a+b\).

**Hint**: The series is an arithmetic-geometric progression.