Walter and Louisa are 65 and 63 years of age respectively and have been married for 27 years. Walter has been working for 34 years; Louisa has been working for 29 years. Walter is entitled to a CPP retirement benefit of $850; Louisa qualifies for a benefit of $460. If Walter and Louisa apply to assign their CPP retirement benefits, by what amount will Louisa's benefit increase from its current level? (Assume the following: Walter has an assignment ratio of 79.41%; his assignable amount is $674.99 and his non-assignable amount is $175.01)

a) $123.37
b) $428.26
c) $551.63
d) $583.37