Since this problem is an identity in k, we first solve the given expression for k.
Literal
This problem [topic-は] k [about-についての] identity [copula-なので], first given-expression [obj-を], k [about-について], solve [polite-ます].
恒等式 'identity' is a mathematical term for an equation true for all values of the variable. 与式 'given expression' is textbook shorthand (与 'given' + 式 'expression'). The sentence exemplifies Japanese technical/academic prose — polite form (ます) but otherwise stripped down, with the logical structure 'since X, therefore Y' using ので.