。
My shoelace came untied.
Literal
Shoelace [subject-が] came-untied.
A short intransitive sentence. 解ける (とける, 'to come untied, be solved, melt') is the intransitive pair of 解く ('to untie, solve'). Note that 解ける shares its reading with 溶ける ('to melt') and 融ける ('to dissolve'); context usually disambiguates. Here the subject is 靴ひも ('shoelace') so the meaning is clear.