public String mulHelper(String num, char c, int power) {
		StringBuffer sb = new StringBuffer();

		if (c == '0') {
			return "0";
		}

		int m = (c - '0');

		int carry = 0;
		for (int i = num.length() - 1; i >= 0; i--) {
			char cc = num.charAt(i);
			int i1 = (cc - '0');
			int r = i1 * m + carry;
			if (r >= 10) {
				sb.append(r % 10);
				carry = r / 10;
			} else {
				sb.append(r);
				carry = 0;
			}
		}
		
		if (carry!=0) {
			sb.append(carry);
		}

		sb = sb.reverse();
		for (int i = 1; i < power; i++) {
			sb.append("0");
		}

		return sb.toString();
	}