Recently, Merca introduced a function \(a_{m,1}^{+}(n)\) , where \(m a_{m,1}^{+}(n)\) is the sum of the parts congruent to 0 modulo m in all the partitions of n. Very recently, several conjectures of Merca on congruences modulo 2 for \(a_{m,1}^{+}(n)\) have been proved by Zhang, Liu and Yao. In this paper, we prove two conjectures of Merca on congruences modulo 3 for \(a_{7,1}^{+}(n)\) and \(a_{25,1}^{+}(n)\) using some identities due to Ramanujan and the theory of modular forms.
