View Compilation Error

0_0_25241813_25889.cpp: In function 'int main()':
0_0_25241813_25889.cpp:84:35: error: invalid initialization of non-const reference of type 'll& {aka long long int&}' from an rvalue of type 'll {aka long long int}'
    res += solve(ri, i) - solve(le - 1, i);
                                   ^
0_0_25241813_25889.cpp:60:4: note: in passing argument 1 of 'll solve(ll&, int&)'
 ll solve(ll &x, int &dig)
    ^