1. **Stating the problem:** We have two arithmetic sequences representing daily targets for two projects over 15 days. - Project A: First day target $a_1=30$, on day 8 target $a_8=58$. - Project B: First day target $b_1=10$, daily increase same as Project A. We need to find total targets for 15 days for both projects and verify given statements. 2. **Formula and rules:** For an arithmetic sequence, the $n$-th term is: $$a_n = a_1 + (n-1)d$$ Total sum of $n$ terms: $$S_n = \frac{n}{2}(2a_1 + (n-1)d)$$ where $d$ is the common difference. 3. **Find common difference $d$ for Project A:** Given $a_8=58$: $$58 = 30 + (8-1)d$$ $$58 = 30 + 7d$$ $$7d = 28$$ $$d = 4$$ 4. **Calculate total for Project A over 15 days:** $$S_{15} = \frac{15}{2}(2 \times 30 + (15-1) \times 4)$$ $$= \frac{15}{2}(60 + 56) = \frac{15}{2} \times 116 = 15 \times 58 = 870$$ 5. **Project B has same difference $d=4$, first term $b_1=10$:** Calculate total for Project B over 15 days: $$S_{15} = \frac{15}{2}(2 \times 10 + (15-1) \times 4)$$ $$= \frac{15}{2}(20 + 56) = \frac{15}{2} \times 76 = 15 \times 38 = 570$$ 6. **Check statements:** - Total Project A = 870 tiang (True) - Total both projects = 870 + 570 = 1440 tiang (Given 1400, so False) - Difference = 870 - 570 = 300 tiang (True) **Final answers:** - Total tiang Project A is 870: **Benar** - Total tiang both projects is 1400: **Salah** (actual 1440) - Difference is 300: **Benar**