Without knowing anything about the sequence, this is impossible to answer. But suppose the sequence is arithmetic, in which case each term differs by some constant [tex]k[/tex]:
[tex]a_2=a_1+k[/tex]
[tex]a_3=a_2+k=a_1+2k[/tex]
[tex]a_4=a_3+k=a_1+3k[/tex]
[tex]\ldots[/tex]
[tex]a_n=a_{n-1}+k=a_1+(n-1)k[/tex]
Then we can write
[tex]a_4+a_8+a_{12}+a_{16}=4a_1+36k=224\implies a_1+9k=56[/tex]
and from the formula above, we see this means the 10th term in the sequence is [tex]a_{10}=56[/tex]. But that's all the specific info we can gather about such an arithmetic sequence. If we set the first term to be some unknown [tex]a_1=a[/tex], then the sum of the first 19 terms in the sequence would be
[tex]\displaystyle\sum_{n=1}^{19}a_n=\sum_{n=1}^{19}\big(a+(n-1)k\big)=19a+k\sum_{n=1}^{18}n=19a+171k[/tex]
If we knew one more term in the sequence, we could determine the value of [tex]k[/tex] and derive the value of [tex]a[/tex] (if the first term [tex]a_1[/tex] is not immediately given), and then go on to find an exact numeric value for the sum.
